wip/refactor credhub service broker

[ctlong]

Are you submitting this PR against the develop branch?

All PR's to CATs should be submitted to develop and will be merged to main once they've passed acceptance.

What is this change about?

Describe the change and why it's needed.

Please provide contextual information.

Include any links to other PRs, stories, slack discussions, etc... that will help establish context.

What version of cf-deployment have you run this cf-acceptance-test change against?

Please check all that apply for this PR:

• introduces a new test --- Are you sure everyone should be running this test?
• changes an existing test
• requires an update to a CATs integration-config

Did you update the README as appropriate for this change?

• YES
• N/A

If you are introducing a new acceptance test, what is your rationale for including it CATs rather than your own acceptance test suite?

CATs should validate common operator workflows.
CATs is not a regression test suite.
CATs is run by every component team to validate their releases before promotion.

How many more (or fewer) seconds of runtime will this change introduce to CATs?

What is the level of urgency for publishing this change?

• Urgent - unblocks current or future work
• Slightly Less than Urgent

Tag your pair, your PM, and/or team!

It's helpful to tag a few other folks on your team or your team alias in case we need to follow up later.