Add support for collecting arbitrary metrics from a textfile as well as
metrics collected from fail2ban. This allows other data to be exported
along with the fail2ban metrics (e.g. instance metadata).
Update the docker image to allow mounting a folder with a collection of
metric files to be exported. Only files ending in `.prom` with be read.
Update project README with the new functionality.
Add a new metric to count the number of database errors that have been
found since startup. This complements the `up` metric to have better
visibility into occasional database errors.
Add a new prometheus metric to track which jails are currently enabled.
Add a new database query to read the jail name and enabled status from the
database.
Add new metric to readme file.
