Refreshing sidebar should have a status indicator

Checklist

• I'm using the latest version of the extension (see the latest version in the right column of this page)
  • Extension version: Put your extension version here
• I'm using the latest VS Code version (find the latest version here)
  • VS Code version: Put your VS Code version here
• I'm using a supported version of GitLab (see README for the supported version)
  • GitLab version: Put your GitLab version here, or say "happens on gitlab.com"

Summary

The GitLab tab in the sidebar has a tool button for refreshing the contents of the sidebar (specifically the pipeline). Pressing this button will update the sidebar after the requests have finished, but there is no indication that requests are underway.

Steps to reproduce

Press the "Refresh sidebar" button in the sidebar.

What is the current bug behavior?

No indication that a refresh is in progress.

What is the expected correct behavior?

Some visual indication that a refresh is in progress.