[Feature]To take out of sync full/delta snapshot, delegate the incoming http request from backup Follower to the backup Leader.

[ishan16696]

Feature (What you would like to be added):
If backup-restore Follower receives the HTTP/HTTPS requests to take out-of-sync full/delta snapshot then delegate that incoming request to the backup-restore Leader and Let the backup-restore leader take/upload the out-of-sync snapshot(full as well as incremental).

Motivation (Why is this needed?):
While adding support to bring the snapshotters (both full and incremental) go routines under the control of the leader-election as described here, We observed that all backup-restore Follower's http handler don't have updated SnapshotterState, if the request comes to the REST endpoints fo follower to take out of sync full/delta snapshot then the snapshot taken will not be the latest, and it is not good to let backup-restore Follower take the snapshot, it should delegate the request to backup-restore Leader.

Approach/Hint to the implement solution (optional):

[ishan16696]

Approach: Get the backup-restore Leader URL and have a reverse proxy on it. so, using this reverse proxy we can able to delegate the incoming HTTP/HTTPS requests from backup-restore Follower to backup-restore Leader.
Using NewSingleHostReverseProxy get the reverse proxy obj which help us to serve the incoming HTTP request.

[timuthy]

Using NewSingleHostReverseProxy get the reverse proxy obj which help us to serve the incoming HTTP request.

Can you explain how the follower knows about the target URL of the leader?

[ishan16696]

I have already implemented this feature in this commit of this leader-election PR. Please refer to this func call.