feat: added pid filtering searchbox and selection counter in snapshot download popup

[sfiorani]

This PR updates what was contributed in #5617 with the following updates:

• Added a searchbox in the snapshot download popup that allows filtering the pids in the checboxes list to easily find the desired ones
• Updated the anchor that select/remove all selections, so when the pid list is filtered with the search box, the anchor select/remove all the filtered and visible checkboxes
• Added a label at the right that indicates the number of pids selected over the total number
• Imrpved the backend that filters the pids checkboxes

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