Move fetch instrumentation from JS contrib to this repo

[david-luna]

Sub-issue of #209

Move the @opentelemetry/instrumentation-document-load instrumentation from opentelemetry-js-contrib

We will follow the decisions made in the move of other instrumentations like fetch (issue)

• should be part of the instrumentation package
• any required util should be moved there
• use logs instead of Span events. Integrate with resource-timing instrumentation with the results of the proposal in Sharing context between network instrumentations and resource timing instrumentation #312