[issue_tracker] batch mode - follow up

[regisoc]

Follow up on #9339

After the great work introduced by @ay-bh , here are the missing points and enhancements to do:

Points for next PR, ordered by priority:

• [x] assignee/watchers changes in comment modal.
• [ ] #9422
• [ ] Change the switch mode button to another, more convenient location. Maybe close to new issue (button only appearing with the right permission).
• [ ] #9423

• [x] site change in card main panel.

Points later on (because not part of the original ticket/issue, but still important):

• [ ] stress test i.e. push 1k, 5k, 10k, 20k, 50k issues with various number of comments and see how the feature behaves.
• [ ] order card elements in main panel.
• [ ] batch-close multiple issues at once.
• [ ] Updates to Readme and Test Plan for the Issue Tracker module

[christinerogers]

Other nice to haves:

• Sortable (not just filtered) Very far off improvements:
• User filter pill elements to highlight and allow quick-cancel of active filters (used in the Open MNI iEEG Atlas)
• better space utilization of the left margin can the left margin