UX: Redesign the "Add credential" feature

[mxr576]

Is your feature request related to a problem? Please describe.

The current implementation of the "Add credential" feature (which was introduced in #446) picks the last created approved credentials in an app add creates a new one based on that credential.

The problems:

• the implemented logic is unclear for end users, especially when an app has multiple credentials and some of them are revoked or expired - Apigee API backend also tends to return credentials in random-ish order.
• Could lead to confusing issues like the one that was reported Cannot ADD KEY when all Credentials are Revoked #773
• Why end users cannot choose which credential they would like to duplicate in an app?

Describe the solution you would like

The "global", app-level "Add credential" button should be replaced with a new, credential-level operation like "Duplicate".

Describe alternatives you have considered

Additional context

Since this is a major UI tweak, it can only be introduced in the current major version if there is gonna be a feature flag for switching between the old and the new implementation.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[mxr576]

@giteshk Hi, can we keep this open?

(and how the "stale bot" configurations could be improved? :) I'd configure it in a way to keep issues/PRs open until no maintainer responded anything. After that, it could be closed if there is no activity by neither the author nor maintainers )

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.