enable linter using golangci-lint across
codebase to run a bunch of linters together,
we shall enable new linters as we fix more
things the codebase.
This PR fixes the first stage of this
cleanup.
This PR also fixes issues when
deletePolicy, deleteUser is idempotent so can lead to
issues when client can prematurely timeout, so a retry
call error response should be ignored when call returns
http.StatusNotFound
Fixes#9347
This is to improve responsiveness for all
admin API operations and allowing callers
to cancel any on-going admin operations,
if they happen to be waiting too long.
