Clean up control plane metrics names

[zhaohuabing]

Original comment on #3564 (comment)

There are two different naming styles in EG:

xds_snapshot_creation_total
xds_snapshot_creation_failed
xds_snapshot_creation_success

status_update_total
status_update_failed_total
status_update_success_total
status_update_conflict_total

Prefer the first one. We also need to align "failed, failure, error" to a single term.

[shawnh2]

Like https://prometheus.io/docs/practices/naming/#labels suggest, we can consider various status like failed, succeed, etc as a label value, this will reduce redundancy.

[arkodg]

thanks for looking into this one @shawnh2, can you revisit the naming for all our control plane metrics and update it based on best practices
cc @Xunzhuo