Rewrite init script (#178)

These changes rewrite the init script to be error aware, informative and have a bit more security awareness.

During rewrite several hidden bugs could be identified and fixed, such as:

- LDAP configuration options interpreted by the shell before passed to command
- Finding multiple ldap ids instead of one during lookup when their names are almost identical
e.g. `_my-ldap-auth` and `my-ldap-auth`
- Properly filter auth sources by their types to prevent unintended type converting attempts that fail

In addition to that the script is a bit cleaner. Some commands do not exist anymore and would cause false-positive errors during script execution.

Helps for: #149

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/178
Reviewed-by: luhahn <luhahn@noreply.gitea.io>
Reviewed-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: justusbunsi <justusbunsi@noreply.gitea.io>
Co-committed-by: justusbunsi <justusbunsi@noreply.gitea.io>

README.md

@@ -356,6 +356,14 @@ gitea:
       existingSecret: gitea-ldap-secret
 ```
 
+:warning: Some options are just flags and therefore don't any values. If they are defined in `gitea.ldap` configuration, they will be passed to the gitea cli without any value. Affected options:
+
+- notActive | not-active
+- skipTlsVerify | skip-tls-verify
+- allowDeactivateAll | allow-deactivate-all
+- synchronizeUsers | synchronize-users
+- attributesInBind | attributes-in-bind
+
 ### OAuth2 Settings
 
 Like the admin user, OAuth2 settings can be updated and disabled but not deleted. Deleting OAuth2 settings has to be done in the ui.