Improve test coverage for Cloud Foundry inputs

[jsoriano]

Currently the only tests for Cloud Foundry are integration tests that need to be run manually. They are ok when changes are done in Cloud Foundry specific code, but other refactors may overlook issues introduced there.

Having an integration test scenario with a real environment is expensive and time consuming, it'd be good to have tests that can be run locally and in CI without requiring a whole environment.

An approximation to this can be with the use of mocks, as other projects do.

Follow up of #28277.

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!