Implement custom Rspec matcher for ROP main classes

MR: Implement custom rop rspec matcher (!153367 - merged)

Description

The following discussion from !147718 (merged) should be addressed:

• @pslaughter started a discussion: (+2 comments)

  I'm assuming this pipeline is covered by an integration test, and we already have Result unit tested, and these individual functions are unit tested. As far as creator_spec coverage goes, from a unit test perspective, I think we're mostly concerned about:

  To assert that the Railway was created and executed as expected, it'd be nice to have helpers like:

  expect_railway_to_have_been_called(
    PersonalAccessTokenCreator.method(:create),
    WorkspaceCreator.method(:create),
    WorkspaceVariablesCreator.method(:create)
  ).with(init_value).and_return(Result.ok(updated_value))

  Then we can greatly reduce the amount of test code here and in other places. WDYT? I think simplifying the testability is one of the best wins we get with ROP.

See entire thread for a more detailed discussion.

See https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/lib/remote_development/README.md#railway-oriented-programming-and-the-result-class for more context on ROP.

Acceptance Criteria

• Define expect_railway_to_have_been_called or similarly named helper in existing ROP helpers in ee/spec/support/helpers/remote_development/railway_oriented_programming_helpers.rb.
• Update all existing ROP unit tests to use the helper where possible

Technical Requirements

• Define the helper as described, in existing ROP helpers in ee/spec/support/helpers/remote_development/railway_oriented_programming_helpers.rb.

Impact Assessment

Improves developer productivity and happiness by making ROP tests easier to write, understand, and maintain.