sdk: Fix double bootstrap

[BillCarsonFr]

Fixes #2998

Changes:

• First commit: init cross-signing with other e2e initial task
  In existing code the bootstraping is done in different places, bootstrap_cross_signing_if_needed or run_intialization_tasks and both are based on the same EncryptionSettings. bootstrap_cross_signing_if_needed was done by LoginBuilder but run_intialization_tasks by MatrixAuth. I propose to move all under run_intialization_tasks that has already support to do it in background, and to call it in one place only: MatrixA uth

• Second commit quick fix (dirty) to avoid having the auth client bootstraping with an in memory olmMachine before creating the final client (finalize_client)

• Public API changes documented in changelogs (optional)

Signed-off-by:

[bnjbvr]

As said in private conversation and dev room, I don't think the workaround is fine. I appreciate you taking the time to track it down and working around it, but we have an overdue refactoring in this area of the code.

[BillCarsonFr]

Bootstrap refactoring moved into separate PR #3024

[bnjbvr]

Closing this one, since the workaround isn't something we want + the interesting refactoring has been split up and merged (thanks!).