Add links to libraries in metadata.yaml

[jaydeluca]

As part of #13468 it would be nice to have links to things like the library source code or documentation for easy reference. It would also be useful when we eventually push some of this information to the opentelemetry.io registry which includes links to websites/documentation.

In the future it might make sense to create a more generic "links" section that allows freeform name/URL pairs, but these two seem appropriate as a starting point. We'll format the resulting output the same so that if we implement the free-form input in the future it won't be a breaking change in terms of the resulting instrumentation list content.

Going through and populating this field for each module can be handled in a followup issue.

Requirements:

• Add new conditional fields to the meta data object for library_source_code, library_documentation
• Update the parsers
• Update the yamlhelper output to include this information in the resulting yaml

The metadata file might look like:

description: This instrumentation provides .....
library_source_code: https://github.com/myLibrary/libraryName
library_documentation: https://mylibrary.website

and the resulting instrumentation-list.yaml:

my-library:
  - name: my-library-0.5
    description: This instrumentation provides .....
    source_path: instrumentation/my-library-0.5
    scope:
      name: io.opentelemetry.my-library-0.5
    target_versions:
      javaagent:
        - com.mylibrary.client:my-library:[0.5.0,)
    links:
      - name: Documentation
        value: https://mylibrary.website
      - name: Source Code
        value: https://github.com/myLibrary/libraryName