metric consolidation for http2/http3

[mrnetops]

Similar to how we consolidated

• tls_v10
• tls_v11
• tls_v12
• tls_v13 into fastly_rt_tls_total{tls_version=$version}

We should consolidate

• http2
• http3
• and the silent but implicit http1 into fastly_rt_http_total {version=$version}.

Right now we need to do hinky things like

sum(rate(fastly_rt_requests_total{}[1m])) 
- sum(rate(fastly_rt_http2_total{}[1m]))
- sum(rate(fastly_rt_http3_total{}[1m])) 

to derive http1 requests and it requires us to explicitly know every potential metric name in play to essentially derive it by exclusion.

i.e. if http4 is added, the above exclusion calculation breaks unless it is explicitly adjusted.

fastly_rt_http_total {version=1} would be soooo much nicer and way less fragile.