KV set_with_meta timing Prometheus histogram is inconsistent

The metric:

kv_set_with_meta_seconds{}

(equivalent to the set_with_meta histogram in cbstats timings)

is inconsistent with all other operation time taken histograms:

kv_cmd_time_taken_seconds{op="get"}

kv_cmd_time_taken_seconds{op="set"}

kv_cmd_time_taken_seconds{op="get_stats"}

and so on.

It should be named similarly:

kv_cmd_time_taken_seconds{op="set_with_meta"}

This will need coordination with ns_server to update the backwards compat mapping.

Update

kv_cmd_time_taken_seconds histograms have all been removed as part of MB-44496, this metric should also be removed, rather than being renamed.