When origin uses broker, have director redirect clients to cache for writes and listings

[bbockelm]

When the origin is behind a connection broker, the cache can connect to it - but normal clients can't. Since caches can proxy directory listings and writes (assuming xrootd/xrootd#2472 is applied), when in this mode the director should redirect the client to a nearby cache for listings and writes.

We may need to version gate this. Assuming v7.18.0 is the first version with the correct XRootD dependency for this functionality, then the director should ensure that the cache being used for proxying is at least v71.18.

Note: please coordinate with @matyasselmeci to make sure xrootd/xrootd#2472 is in the Pelican xrootd build. Given writes don't work at all with the origin in broker mode, we can ignore backward compatibility issues.

[matyasselmeci]

PelicanPlatform/xrootd#32 for adding the patch to our XRootD build.

[matyasselmeci]

@jhiemstrawisc , xrootd-5.8.3-1.3 includes that patch and has passed our automated tests so it's ready for you to try out.

[github-actions]

This issue is stale because it has been open for 60 days with no activity.