Use canonical link cleanup

[chalin]

• Use connectrpc.com instead of connect.build
  • Update semconv - [editorial] Use canonical URL to connectrpc.com instead of connect.build semantic-conventions#1933
  • Update OTel Go (Go has an archive of semconv, we won't be touching the URLs in those.)
• Use https://unitsofmeasure.org/ucum instead of http://unitsofmeasure.org/ucum, which redirects
  • [editorial] Update metrics.proto comment to use https opentelemetry-proto#632
  • [editorial] Use canonical https URLs semantic-conventions#1934
• [CI] Report http scheme in URL unless localhost, fix links #6411
• Update refcache
  • Drop entries using old URL, esp. the http reference http://connect.build (it should be https).
  • While we're there, drop http://docs.oasis-open.org/security/saml/Post2.0/sstc-saml-tech-overview-2.0.html once semconv is updated.