Validate project key presence if Jira issues enabled

What does this MR do?

As part of the Jira issues integration &3622 (closed) we need to validate the presence of the project key when enabling the Jira issues.

This is a EE feature.

Apart from the backend validation, we are also going to add this validation on the frontend side !36725 (merged) and !36860 (merged).

Related to #228634 (closed), #223787 (closed)