feat(cpp): add functions related to client lifecycle, and message headers

[slbotbm]

Which issue does this PR address?

Closes #
Relates to #2100

Rationale

Contributes to completion of cpp sdk.

What changed?

added user header handling, and the following functions:

• disconnect
• shutdown
• delete_segments
• get_cluster_metadata
• update_permissions
• change_password

Local Execution

• Passed
• Pre-commit hooks ran

AI Usage

If AI tools were used, please answer:

1. Which tools? codex
2. Scope of usage? code generation, code investigation
3. How did you verify the generated code works correctly? read through it, tested it.
4. Can you explain every line of the code if asked? yes

[github-actions]

Thanks for the PR. It is labeled S-waiting-on-review and queued for review.

Slash commands (own line, regular comment) move it around the queue:

• /ready - back to S-waiting-on-review after addressing feedback
• /author - flip to S-waiting-on-author while you finish changes
• /request-review @user-or-team - request a reviewer

See CONTRIBUTING.md for details.