feat(instrumentation-document-load): documentLoad attributes enhancement

[kkruk-sumo]

Which problem is this PR solving?

This PR answers questions:

• which website has been loaded (added http.url and page_title),
• who visited it (added http.user_agent).

[kkruk-sumo]

documentLoad span is the root one so I think previous names were mistaken?

[codecov]

Codecov Report

Merging #433 (c644641) into main (b128dae) will increase coverage by 3.83%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main     #433      +/-   ##
==========================================
+ Coverage   92.00%   95.83%   +3.83%     
==========================================
  Files           2       15      +13     
  Lines          25      624     +599     
  Branches        4       94      +90     
==========================================
+ Hits           23      598     +575     
- Misses          2       26      +24     

Impacted Files	Coverage Δ
...metry-propagator-aws-xray/src/AWSXRayPropagator.ts	100.00% <0.00%> (ø)
...propagator-aws-xray/test/AWSXRayPropagator.test.ts	100.00% <0.00%> (ø)
packages/opentelemetry-host-metrics/src/metric.ts	100.00% <0.00%> (ø)
...ages/opentelemetry-host-metrics/src/BaseMetrics.ts	57.57% <0.00%> (ø)
packages/opentelemetry-host-metrics/src/enum.ts	100.00% <0.00%> (ø)
...ackages/opentelemetry-host-metrics/src/stats/si.ts	66.66% <0.00%> (ø)
...metry-propagator-ot-trace/src/OTTracePropagator.ts	95.83% <0.00%> (ø)
...s/opentelemetry-propagator-ot-trace/src/version.ts	0.00% <0.00%> (ø)
packages/opentelemetry-host-metrics/src/version.ts	100.00% <0.00%> (ø)
...ges/opentelemetry-host-metrics/test/metric.test.ts	96.52% <0.00%> (ø)
... and 3 more

[kkruk-sumo]

I messed up branch in fork repo so here is the re-created PR: #441 .