[JENKINS-56830] alternative use of 'html_url' in payload of event

[McFoggy]

As documented in github API docs (https://developer.github.com/v3/repos/#response) the url field of the event should/could point to the API endpoint.
In the github-plugin it is expected to work on the public html url which is handled by the 'html_url' field of the event.
This commit thus try as before to build a GitHubRepositoryName from the 'url' field ; if that fails, as a fallback it also tries the 'html_url' field.
See also https://github.community/t5/GitHub-API-Development-and/consistency-of-repository-url-between-event-types/td-p/21209 for some explanations.

---

This change is 

[KostyaSha]

logger

[McFoggy]

@KostyaSha modification done as as requested ; please look at latest push. Thx

[KostyaSha]

lgtm

[solvingj]

This should have printed it's message with Logger.warning() because currently, if this alternate path is taken, the last message in the default system log is:

WARNING c.c.jenkins.GitHubRepositoryName#create: Could not match URL

Which would seem like it's the end of the road for this PUSH hook being processed. But, adding a custom logger and turning up the debug level, we can see this happening after:

PushEvent handling: 'html_url' field has been used to retrieve project information (instead of default 'url' field)

Which indicates that in-fact, we did in-fact successfully create a GitHubRepositoryName and assign it to fromEventRepository.

Unfortunately, builds still do not trigger on this path. But, this comment is only to suggest changing the log level here.