Website: support GH page links to canonical src

[chalin]

Contributes to open-telemetry/opentelemetry.io#542

/cc @carlosalberto @mtwo @shelbyspees @austinlparker

While I can't (currently) show you a preview of this PR, you can see the corresponding change for OTel Java (open-telemetry/opentelemetry-java#3501) in action by trying the Edit this page and related links, from https://opentelemetry.io/docs/java/ and it's subpages.

@Aneurysm9 @MrAlias: I see that this repo doesn't yet have a docs-update GitHub action. I'm going to try an alternative approach that doesn't require an action. If it doesn't work, or isn't approved, I'll submit a docs-update workflow (and get an appropriate token) -- FYI.

[codecov]

Codecov Report

Merging #2189 (6786f86) into main (6da20a2) will increase coverage by 0.0%.
The diff coverage is n/a.

@@          Coverage Diff          @@
##            main   #2189   +/-   ##
=====================================
  Coverage   72.8%   72.8%           
=====================================
  Files        177     177           
  Lines      12151   12151           
=====================================
+ Hits        8852    8855    +3     
+ Misses      3060    3058    -2     
+ Partials     239     238    -1     

Impacted Files	Coverage Δ
...s/otlp/otlptrace/internal/connection/connection.go	16.4% <0.0%> (+1.5%)	⬆️