v3 should allow to update docker registry credentials

[kathap]

CAPI issue: #3304 Missing v3 feature parity.

PATCH /v3/packages/:guid should allow to update docker registry credentials.

This change adds the possibility to update the docker credentials via PATCH /v3/packages/:guid. After the PATCH the user has to restage the app in order to compile a new droplet with the new credentials.

• Links to any other associated PRs
  Docker's registry password #3304
  Adapt update docker credentials part docs-dev-guide#494

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• I have made this pull request to the main branch

• I have run all the unit tests using bundle exec rake

• I have run CF Acceptance Tests

[moleske]

Can you update the docs to show this new support for username and password?

Otherwise seems good. You could consider adding a test at the controller integration level if you wanted to test the flow the whole way through (this test file.) This would allow you to exercise the whole flow with real components, but some might consider it too much for this change. I can probably be convinced either way

[kathap]

Can you update the docs to show this new support for username and password?

Otherwise seems good. You could consider adding a test at the controller integration level if you wanted to test the flow the whole way through (this test file.) This would allow you to exercise the whole flow with real components, but some might consider it too much for this change. I can probably be convinced either way

Sure, documentation will be updated. Maybe I set it to draft, still working on tests and cases where only password or username is updated :)
Maybe also this documentation needs then an update..

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[kathap]

Tested the new PATCH, works with a restage after the PATCH, you can update username and password or just one of them.