Integrating remoting 2.53.2

[FIX SECURITY-234] Abort plugin/core update on checksum mismatch

[FIX SECURITY-233] Remove multipart form exception from crumb filter

[FIX SECURITY-225] Add RequirePOST annotations

[FIX SECURITY-95] Add CSP headers to files served by Jenkins

[SECURITY-218] - Functional tests for CLI

[SECURITY-218] Blackbox test

Trying to touch userContent rather than some random file, so that we can verify the result remotely.
Reducing rounds to two: one for capability, one for random transport commands.

This is intended to be a true blackbox test: while we customize the client behavior, it can run against any server.