Provide consistent database configuration capabilities

[jonathanlukas]

Describe the use case:

As infrastructure engineer, I have to configure multiple database connections as of now:

• Identity
• Web Modeler

These database connections offer different properties:

Identity:

key	explanation	default value
identity.externalDatabase.enabled		false
identity.externalDatabase.host	Database host	nil
identity.externalDatabase.port	Database port number	nil
identity.externalDatabase.username	Non-root username	nil
identity.externalDatabase.password	Password for the non-root username	nil
identity.externalDatabase.database	The database name	nil
identity.externalDatabase.existingSecret	Name of an existing secret resource containing the database credentials	nil
identity.externalDatabase.existingSecretPasswordKey	Name of an existing secret key containing the database credentials	nil

web modeler:

key	explanation	default value
webModeler.restapi.externalDatabase	can be used to configure a connection to an external database; will only be applied if the postgresql dependency chart is disabled (with postgresql.enabled=false)
webModeler.restapi.externalDatabase.url	defines the JDBC url of the database instance	""
webModeler.restapi.externalDatabase.user	defines the database user	""
webModeler.restapi.externalDatabase.password	can be used to provide the database user's password; ignored if webModeler.restapi.externalDatabase.existingSecret is set	""
webModeler.restapi.externalDatabase.existingSecret	can be used to provide the name of an existing secret resource containing the database password	nil
webModeler.restapi.externalDatabase.existingSecretPasswordKey	can be used to provide the name of an existing secret key containing the database password	""

Describe the enhancement/feature:

Please provide a consistent set of keys:

• enabled (implicit in web modeler as of now, explicit in identity) -> implicit for both OR explicit for both
• url (allows more flexibility than host-port-database)
• username (is user for web modeler as of now)
• password
• existingSecret
• existingSecretPasswordKey

Hint: For identity, host, port and database are simply condatinated...

https://github.com/camunda/camunda-platform-helm/blob/main/charts/camunda-platform-latest/templates/identity/configmap.yaml#L272

Desired outcome and acceptance tests:

Both sections identity.externalDatabase AND webModeler.restapi.externalDatabase should be configurable in the exact same way.