test(e2e): add test harness for Temporal Cloud

[tomba7]

Closes #11

What was changed

• Added an e2e harness for testing against a real Temporal Cloud account:
• scripts/e2e/e2e-cloud, checks, creates and deletes test namespaces.
• make test-cloud-preflight, checks the API key and its access.
• make test-cloud-harness, runs test/e2e/harness/cloud-basic.yaml, which creates, checks and deletes a namespace without the operator.
• Each run gets a run ID.
• Test namespaces created with the harness are makred with a description that records the manager (resouce operator), run ID and owner (local username, CI can override with TEST_CLOUD_OWNER).

Why?

Upcoming features need to manage real Cloud resources and a reliable E2E test harness is required.

Tradeoffs considered

• Picked a simpler bash script (vs developing a Go tool) to validate the Temporal Cloud resources for speed and ease. This can be swapped with a Go tool that uses the same shared connection library as the operator in later commits.
• Multiple ways to generate a unique namespace ID for each test run. I picked tro-e2e-<run ID>-<suffix> for simplicty, make room for a suffix if needed and still stay under the 39 char limit.

Note: This is a larger PR rather than several small ones because the pieces only make sense together.