[pgAdmin][RM7404] Port process watcher to React

Hi Hackers,

This patch essentially implements #3709 along with moving the process watcher to React. The patch includes:

1. Add a new tab "Processes" to view and manage all the background processes.

2. Processes tab allows to stop processes, remove process info and logs, and view process logs and other details.

3. The process watcher is removed. Instead, it will just notify if a process is started, terminated, failed or completed. It will have a button "View Processes" which will take you to the processes tab.

4. New page of processes is added to the documentation and other pages updated.

5. JS Test cases added.

Please review.