fix(server): Added validation for duplicated link config names

[ffuerste]

Feature or Problem

If an application manifest is applied in which several link configurations have the same name, this leads to a dead loop.

Related Issues

closes #478

Release Information

This PR fixes a problem without making any breaking changes. It can therefore be safely included in the next version.

Consumer Impact

This PR introduces an additional validation logic that prevents users to apply invalid manifests. If the manifest is valid, nothing changes for the users.

Additionally, it is planned to modify the BackoffWrapper and introduce an exponentially increasing delay for a retry in case of an error, which introduces longer feedback loops for (debugging) users.

Testing

Unit Test(s)

Acceptance or Integration

An additional test case has been added for the new validation logic.

Note: Further tests may be added as part of the “BackoffWrapper” modification.

[ffuerste]

@brooksmtownsend I created a draft PR for the first part of your suggestion. So that you can already review it.

Meanwhile I will look into the BackoffWrapper idea and update the PR accordingly.

Many thanks.

[brooksmtownsend]

Great work @ffuerste ! I think we could get this one ready for review and merge as-is as the individual feature if you're interested, rather than adding on the BackoffWrapper bit here.

I left a really small nit that you can address if you need to push up any additional fixes, but it's fine to just leave it as-is as well. Feel free to mark it as resolved once you feel it's fixed or that it is not necessary and we can merge.

[ffuerste]

@brooksmtownsend Many thanks for the review!

I agree, I think it is better to merge the validation logic as an individual feature for now. Figuring the BackoffWrapper part out is a little bit tricky for me at the moment. I suggest, that we create maybe another issue for this part?

Therefore, I remove the draft status and this PR can be reviewed from my side.