[TASK] Use new Identity SDK config for Connectors

[chillleader]

Related to:

https://github.com/camunda/product-hub/issues/1969
camunda/connectors#1638

Overview:

Connectors need to be switched to the new Identity SDK config, looking roughly like this:

camunda.identity.type=keycloak
camunda.identity.base-url=http://localhost:8084
camunda.identity.issuer=http://localhost:18080/auth/realms/camunda-platform
camunda.identity.issuer-backend-url=http://localhost:18080/auth/realms/camunda-platform
camunda.identity.audience=connectors
camunda.identity.client-id=xxx
camunda.identity.client-secret=xxx

Actions:

1. Add the new config
2. Remove the old config for authentication with individual components (Zeebe/Operate), as the underlying code now relies on the Identity config.

[aabouzaid]

@chillleader does that change require migration steps during the upgrade from the previous version?

[chillleader]

@aabouzaid No migration steps required

[chillleader]

Done in #1265