Add snapshot delete command to CLI

[strickvl]

Added:

• the zenml pipeline snapshot delete CLI command
• a test for that CLI command
• a docs section covering the new CLI command as well as how to do it with the Python SDK.

[github-actions]

Documentation Link Check Results

❌ Absolute links check failed
There are broken absolute links in the documentation. See workflow logs for details
✅ Relative links check passed
_{Last checked: 2025-10-10 13:44:41 UTC}