Fix ketama quorum (#5910)

* Fix quorum calculation for Ketama hashring

The quorum calculation is currently broken when using the Ketama
hashring. The reasons are explained in detail in issue
#5784.

This commit fixes quorum calculation by tracking successfull writes
for each individual time-series inside a remote-write request.

The commit also removes the replicate() method inside the Handler
and moves the entire logic of fanning out and calculating success
into the fanoutForward() method.

Signed-off-by: Filip Petkovski <[email protected]>

* Fix error propagation

Signed-off-by: fpetkovski <[email protected]>

* Fix writer errors

Signed-off-by: fpetkovski <[email protected]>

* Separate write from replication errors

Signed-off-by: fpetkovski <[email protected]>

* Add back replication metric

Signed-off-by: Filip Petkovski <[email protected]>

* Address PR comments

Signed-off-by: Filip Petkovski <[email protected]>

* Address code review comments

Signed-off-by: Filip Petkovski <[email protected]>

Signed-off-by: Filip Petkovski <[email protected]>
Signed-off-by: fpetkovski <[email protected]>