CASMCMS-9225 as a whole involves changes to a number of different files in BOS. In order to aid with review, I'm breaking the overall thing up into smaller PRs. Each will be built on top of each other, and will be merging into the main PR branch. Only once each sub-PR has been approved and merged will I merge that branch into develop.
Full list of sub-PRs:

1. Added basic paging ability for GET requests to list components
2. Create generic endpoint classes
3. Create generic API client class
4. Create ApiClients class and provide it to BOS operators inside a context manager
5. Move PCS client to new paradigm
6. Move BSS client to new paradigm
7. Move CFS client to new paradigm
8. Move BOS client to new paradigm
9. Move IMS client to new paradigm
10. Move HSM client to new paradigm
11. CHANGELOG update, linting, update utils

This PR creates a generic API client class, built on top of the API endpoint classes from this PR. The APIClient is a subclass of RequestsRetryManager from bos.common.utils, and that is a subclasss of the RequestsRetryManager class from the requests-retry-session Python package.

Basically, the RetrySessionManager class can be used to turn any other class into a context manager that contains a requests session, one that is only initialized if it is used. And this request session (and its underlying HTTP adapter) will both be closed out automatically by the context manager.

The bos.common.utils subclass just specified the default argument values that BOS uses for its requests sessions.

The APIClient subclass includes a method (get_endpoint) which will be used to retrieve endpoints for specific API endpoints. It initializes them on demand, and passes in its managed request session. When used as a context manager, it clears its record of the endpoints that it initialized (because the session they are using is also cleaned up when the context manager exits).

This will be used as the building block for the API clients coming in the next PRs. Right now, this PR does not modify anything to use this client class.