chore: fixing documentation for web tracer provider, fixing examples …

[obecny]

…for web, enable manager when registering

Which problem is this PR solving?

• Fixes Documentation for Web is wrong - the provider is missing the context #905

Short description of the changes

1. The documentation for web was wrong when creating web tracer provider and changing the context manager.
2. Also examples were outdated but also broken due to strange lint fixes.
3. I have also added enabling the context manager when user passes a new one in register
   Without this the manager is being created but in fact it never works and it was quite difficult to finally figure out what was wrong. This way the simplified form of creating new context manager will be easier for a user
   for example this wasn't working - the zone was disabled, now it will be enabled
   provider.register({ contextManager: new ZoneContextManager(), });
   I have also added checking in constructor to throw an error if someone adds either contextManager or propagator into constructor instead of register - as it is currently shown in out documentation for web. This way user will now faster what is wrong.
4. The last fix is in document-load plugin it adds parent to resources loaded during the document load
5. One more fix: the user interaction plugin was broken after the context propagation changes

[codecov-io]

Codecov Report

Merging #906 into master will increase coverage by 0.40%.
The diff coverage is 95.65%.

@@            Coverage Diff             @@
##           master     #906      +/-   ##
==========================================
+ Coverage   94.08%   94.48%   +0.40%     
==========================================
  Files         248      248              
  Lines       10835    10997     +162     
  Branches     1055     1062       +7     
==========================================
+ Hits        10194    10391     +197     
+ Misses        641      606      -35     

Impacted Files	Coverage Δ
...try-plugin-user-interaction/src/userInteraction.ts	92.78% <93.75%> (+4.95%)	⬆️
packages/opentelemetry-core/src/context/context.ts	94.11% <100.00%> (ø)
...telemetry-plugin-document-load/src/documentLoad.ts	98.03% <100.00%> (ø)
...ackages/opentelemetry-web/src/WebTracerProvider.ts	100.00% <100.00%> (ø)
...ntelemetry-tracing/test/MultiSpanProcessor.test.ts	97.43% <0.00%> (-2.57%)	⬇️
packages/opentelemetry-tracing/src/config.ts	100.00% <0.00%> (ø)
packages/opentelemetry-tracing/src/utility.ts	100.00% <0.00%> (ø)
packages/opentelemetry-plugin-https/src/utils.ts	100.00% <0.00%> (ø)
packages/opentelemetry-tracing/test/Span.test.ts	100.00% <0.00%> (ø)
... and 18 more

[mayurkale22]

lgtm, thanks for fixing this.

[obecny]

added more fixes - point 5