Improve gitlab-shell logging structure

Problem

There is no separation in logs between "expected errors" (when user does not have access, for example) and "critical errors" (when something went wrong).

It generates lots of noise and makes it difficult to analyze root causes of server problems. See example: https://gitlab.com/gitlab-com/create-stage/weekly-status-check-in/-/issues/70#note_1241073613.

Proposal

Improve the logging structure.

Add multiple classes of errors:

• SSH connection errors
• Request errors
• Gitaly errors

Add extra information for each error:

• Url
• Project / user information (if available)
• Change error type depending on severity (warn, error, fatal)