Add configure connection list command

[ewega]

Summary

Add a \configure connection list\ subcommand to show all existing connections, useful for scripting, debugging, and answering 'what do I have?'.

Design

\
gh devlake configure connection list
gh devlake configure connection list --plugin gh-copilot # filter by plugin
\\

Output:
\
Plugin ID Name Organization Enterprise
github 1 GitHub - my-org my-org
gh-copilot 2 GitHub Copilot - my-org my-org avocado-corp
\\

Changes

• Add \list\ subcommand under \configure connection\
• Iterate all known plugins, call \GET /plugins/{plugin}/connections\
• Optional --plugin\ filter
• Table-formatted output

Acceptance Criteria

• Lists connections from all available plugins
• --plugin\ flag filters to one plugin
• Shows ID, name, organization, enterprise columns
• Clean output when no connections exist