Add config fallbacks for session, cache and queue when disabling redis-cluster (#585)

### Description of the change

Add config fallbacks for `session`, `cache` and `queue` including tests.

### Benefits

If users disable the default `redis-cluster` sub-chart dependency, this will configure the respective sections to use the Gitea defaults as listed in https://docs.gitea.com/next/administration/config-cheat-sheet.

### Possible drawbacks

Users will run on non-optimal settings for production without knowing their config.

### Applicable issues

  - fixes #584 #573 #489 #476 #468 #453

### Checklist

<!-- [Place an '[X]' (no spaces) in all applicable fields. Please remove unrelated fields.] -->

- [x] Parameters are documented in the `values.yaml` and added to the `README.md` using [readme-generator-for-helm](https://github.com/bitnami-labs/readme-generator-for-helm)
- [x] Breaking changes are documented in the `README.md`
- [x] Templating unittests are added

Co-authored-by: justusbunsi <sk.bunsenbrenner@gmail.com>
Co-authored-by: justusbunsi <justusbunsi@noreply.gitea.com>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/585
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.com>

unittests/config/cache-config.yaml

@@ -0,0 +1,45 @@
+suite: config template | cache config
+release:
+  name: gitea-unittests
+  namespace: testing
+tests:
+  - it: "cache is configured correctly for redis-cluster"
+    template: templates/gitea/config.yaml
+    set:
+      redis-cluster:
+        enabled: true
+    asserts:
+      - documentIndex: 0
+        equal:
+          path: stringData.cache
+          value: |-
+            ADAPTER=redis
+            HOST=redis+cluster://:@gitea-unittests-redis-cluster-headless.testing.svc.cluster.local:6379/0?pool_size=100&idle_timeout=180s&
+
+  - it: "cache is configured correctly for 'memory' when redis-cluster is disabled"
+    template: templates/gitea/config.yaml
+    set:
+      redis-cluster:
+        enabled: false
+    asserts:
+      - documentIndex: 0
+        equal:
+          path: stringData.cache
+          value: |-
+            ADAPTER=memory
+            HOST=
+
+  - it: "cache can be customized when redis-cluster is disabled"
+    template: templates/gitea/config.yaml
+    set:
+      redis-cluster:
+        enabled: false
+      gitea.config.cache.ADAPTER: custom-adapter
+      gitea.config.cache.HOST: custom-host
+    asserts:
+      - documentIndex: 0
+        equal:
+          path: stringData.cache
+          value: |-
+            ADAPTER=custom-adapter
+            HOST=custom-host

unittests/config/queue-config.yaml

@@ -0,0 +1,45 @@
+suite: config template | queue config
+release:
+  name: gitea-unittests
+  namespace: testing
+tests:
+  - it: "queue is configured correctly for redis-cluster"
+    template: templates/gitea/config.yaml
+    set:
+      redis-cluster:
+        enabled: true
+    asserts:
+      - documentIndex: 0
+        equal:
+          path: stringData.queue
+          value: |-
+            CONN_STR=redis+cluster://:@gitea-unittests-redis-cluster-headless.testing.svc.cluster.local:6379/0?pool_size=100&idle_timeout=180s&
+            TYPE=redis
+
+  - it: "queue is configured correctly for 'levelDB' when redis-cluster is disabled"
+    template: templates/gitea/config.yaml
+    set:
+      redis-cluster:
+        enabled: false
+    asserts:
+      - documentIndex: 0
+        equal:
+          path: stringData.queue
+          value: |-
+            CONN_STR=
+            TYPE=level
+
+  - it: "queue can be customized when redis-cluster is disabled"
+    template: templates/gitea/config.yaml
+    set:
+      redis-cluster:
+        enabled: false
+      gitea.config.queue.TYPE: custom-type
+      gitea.config.queue.CONN_STR: custom-connection-string
+    asserts:
+      - documentIndex: 0
+        equal:
+          path: stringData.queue
+          value: |-
+            CONN_STR=custom-connection-string
+            TYPE=custom-type

unittests/config/session-config.yaml

@@ -0,0 +1,45 @@
+suite: config template | session config
+release:
+  name: gitea-unittests
+  namespace: testing
+tests:
+  - it: "session is configured correctly for redis-cluster"
+    template: templates/gitea/config.yaml
+    set:
+      redis-cluster:
+        enabled: true
+    asserts:
+      - documentIndex: 0
+        equal:
+          path: stringData.session
+          value: |-
+            PROVIDER=redis
+            PROVIDER_CONFIG=redis+cluster://:@gitea-unittests-redis-cluster-headless.testing.svc.cluster.local:6379/0?pool_size=100&idle_timeout=180s&
+
+  - it: "session is configured correctly for 'memory' when redis-cluster is disabled"
+    template: templates/gitea/config.yaml
+    set:
+      redis-cluster:
+        enabled: false
+    asserts:
+      - documentIndex: 0
+        equal:
+          path: stringData.session
+          value: |-
+            PROVIDER=memory
+            PROVIDER_CONFIG=
+
+  - it: "session can be customized when redis-cluster is disabled"
+    template: templates/gitea/config.yaml
+    set:
+      redis-cluster:
+        enabled: false
+      gitea.config.session.PROVIDER: custom-provider
+      gitea.config.session.PROVIDER_CONFIG: custom-provider-config
+    asserts:
+      - documentIndex: 0
+        equal:
+          path: stringData.session
+          value: |-
+            PROVIDER=custom-provider
+            PROVIDER_CONFIG=custom-provider-config