Add partial search by usernames to GET /organizations/:guid/users

[a-b]

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A short explanation of the proposed change:

Add partial search by usernames to GET /organizations/:guid/users

For partial_usernames parameter, we are using UAA /Users endpoint that requires scim.read scope.

An explanation of the use cases your change solves

This will let us to find usernames by substring e.g. GET /organizations/:guid/users?partial_usernames=foo

Links to any other associated PRs

CF-D PR

• [x] I have reviewed the contributing guide

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• [x] I have made this pull request to the main branch

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

• [x] I have run CF Acceptance Tests

Coauthored by @jdgonzaleza