Update: support qcs account headers on engagement creation

[erichulburd]

Description

We want to support the client's ability to explicitly set QCS account on the quantum computer they will execute against. To this end, we allow clients to explicitly pass account_id and account_type on get_qc. This will initialize an EngagementManager with account id/type, which, in turn, will set the X-QCS-ACCOUNT-{ID/TYPE} headers on the engagement request. This enables users to identify their QPU job as belonging to a group account.

TODO:

• Run poetry update qcs-api-client and commit poetry.lock

Checklist

• The PR targets the rc branch (not master).
• The above description motivates these changes.
• There is a unit test that covers these changes.
• All new and existing tests pass locally and on the PR's checks.
• Parameters and return values have type hints with PEP 484 syntax.
• Functions and classes have useful Sphinx-style docstrings.
• All code follows Black style and obeys flake8 conventions.
• (New Feature) The docs have been updated accordingly.
• (Bugfix) The associated issue is referenced above using auto-close keywords.
• The changelog is updated, including author and PR number (@username, Test ignore #1234).

[dbanty]

Looks good—my only comment is it seems like the new fields could belong on the config object which is already optionally passed into get_qc and the EngagementManager. Then we don't expand the get_qc signature which is already fairly complicated and the config continues to serve the purpose of modifying QCS calls.

[erichulburd]

Superseded by #1439 to address @dbanty 's comment.