[v2] Add Session IDs to User-Agent header even when cache does not exist

[aemous]

Issue #, if available:

• CLI-8466 (internal)

Description of changes:

• Fixed a bug where session IDs are added to the User-Agent HTTP header even when the local cache does not exist.
• Modified CLISessionDatabaseConnection to allow a cache directory override to be passed in during initialization. This improves testability.
• Added new regression test that verifies (1) local cache is created and (2) database connection succeeds when the local cache does not exist.

Description of tests:

• IN PROGRESS Successfully ran all tests and the pre-production build workflow (see GitHub Actions).
• TODO Run manual commands with the cache deleted beforehand, inspect the user agent header.

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