Add licensing and copyright information for all files in this repository. This
either happens in the file itself as a comment header or in the file
`.reuse/dep5`.
This commit also adds a Github workflow to check pull requests and adapts
copyright.pl to the changes.
Closes#8869
This adds the CURLOPT_TRAILERDATA and CURLOPT_TRAILERFUNCTION
options that allow a callback based approach to sending trailing headers
with chunked transfers.
The test server (sws) was updated to take into account the detection of the
end of transfer in the case of trailing headers presence.
Test 1591 checks that trailing headers can be sent using libcurl.
Closes#3350
