standardize metrics naming

[ilawjr]

Right now our metrics are a hodge-podge of names. For example, here are the names for api requests on our different services:

xmidt_caduceus_api_requests_total
xmidt_petasos_api_requests_total
xmidt_scytale_api_requests_total
xmidt_talaria_api_requests_total

xmidt_argus_server_request_count
xmidt_themis_server_request_count
webpa_tr1d1um_server_request_count

this metric in particular has the job and role labels, so having the server name in the metric itself is redundant. Following a standard naming convention like node_exporter does would make creation and re-use of charts (e.g. grafana) much easier.