Prototype GitLab support for webhooks about experimental HOT 5 CLOSED

Prototyped - implemented and delivered

from experimental.

Please check this knative/eventing-contrib#382
I guess Knative will support gitlab as eventing source soon.

from experimental.

Thanks for the pointer @vincent-pli - that's a huge pull request :-o

from experimental.

Will start looking at this after I finish #362 which will give us a client we can use to talk to different git providers.

from experimental.

I have a very hacked together proof-of-concept for some of this:

My Changes:

1. Create client (GitHub/Gitlab) based on repo URL (as first pass) as create/delete webhook
2. Modify git pipelineresource to take a tlsVerify flag to disable certificate validation on git commands as using a self signed cert.
3. Modified interceptor to look for different headers/values
4. Modified test pipeline triggertemplate/bindings
5. Modified monitor binding for gitlab

Not verified:

6. Monitor task not coded for gitlab - would need changing
7. PullRequest pipelineresource not coded for gitlab - would either need fixing or need monitor task to use gitlab api directly for interactions with the merge request
8. API endpoints not fully investigated

from experimental.