Patch tinyfilemanager to add response headers for metrics

[benoit74]

Rationale

https://github.com/offspot/metrics/ needs to compute the number of files added and removed in the file manager.

Current tinyfilemanager code does not permit to process URLs to detect this information, so we are now patching tinyfilemanager to add response headers when files have been added and removed, with the number of files added / removed.

Changes

• two new global variables $files_added and $files_deleted to store amount of files added or deleted in a given request
• new fm_report_files function which really output the headers when needed
• new fm_count_files function to count files in a given folder
• a X-TFM-Files-Added header is returned with the number of files added (only when files have been added):
  • Upload from URL (~ lines 652-657)
  • Create a new file (~ lines 700-707)
  • Upload file (~ lines 1050-1063), single upload (~ lines 1021-1030) and chunked upload (~ lines 1030-1041)
  • Create a Zip / Tar (~ lines 1141-1155)
  • Extract a Zip / Tar (~ lines 1210-1226) (we needed a new fm_count_files function for that)
  • Mass copy + copy single file (~ lines 2395-2440)
• a X-TFM-Files-Deleted header is returned with the number of files deleted (only when files have been deleted):
  • Mass delete + delete single file (~ lines 2298-2316)

[benoit74]

I was convinced we had test CI in place to confirm image build is OK in PRs too ; I expected to test the build locally (and fix it, because I knew it would be KO) but once I saw the branch is green after I finished to prepare the first comment with all details, I thought "oh, great, I did good job" 🤦🏻

Sorry ...