feat: add prompt management to Python SDK

[uddhavdave]

Changes

• Export PromptStore, PromptBinding, ResolvedPrompt, and PromptError from the SDK.
• Cache text prompts from OpenObserve in memory. Validate names and versions; refresh conditionally via ETags while retaining last-known-good snapshots on refresh failures.
• Document setup, lifecycle, status, and credential handling; add behavioral tests and the HTTPX dependency.

Verification

• Python 3.9: ruff check ., ruff format --check ., mypy openobserve, pytest -q tests (121 passed).
• Matching o2-sre-agent: prompt/configuration/query/telemetry tests (69 passed).

Consumer dependency

The matching o2-sre-agent branch is ud/feat-prompt-mangement. Its registry-based uv.lock cannot be regenerated until openobserve-python-sdk is published; the old telemetry distribution shares the openobserve module namespace and must not be installed alongside it.