[JENKINS-62779] handle proxy hosts exclusions

[thomasgl-orange]

See JENKINS-62779.

This is a follow-up to #124, recently released in 1.5.5. This PR has introduced support for using an HTTP proxy server (the one configured in the Jenkins Update Center settings) when connecting to a GitLab server. But the proxy exclusions settings (the "No Proxy Host" list) is ignored with this implementation. Quoting @jbdelpech:

Unfortunately, ProxyClientConfig does not support no_proxy parameter. At least, there is few chance to have multiple gitlab servers behind proxy and directly reachable.

So, this was actually an improvement for some users, but also a regression for some others:

• people stuck behind a corporate proxy for internet access, who want to reach gitlab.com => 1.5.5 fixes their use case
• people stuck behind a corporate proxy for internet access, who want to reach an internal (on-premise) GitLab server => used to work fine up to 1.5.4, may break with 1.5.5 (if the proxy is restricted to internet only). And deconfiguring the Jenkins Update Center proxy is not an option, since these settings are not specific to the GitLab Branch Source plugin (they're used by many other plugins, by some core features like some tools installers, and by the Update Center itself).

This PR adds support for taking the "no proxy" hosts list into account. We know the target GitLab server host, thus we can test whether it matches the proxy exclusions list or not, and if it does we can avoid passing proxy properties to the gitlab4j API.
A trick for testing the "no proxy" hosts list for a given target host is to use ProxyConfiguration.getNoProxyHostPatterns() (see usage examples).

There are no new unit tests in this PR. I only did minimal manual testing via the "Test Connection" button with different proxy settings, and also checked that existing unit tests are still okay.

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CC for review: @jbdelpech, @markyjackson-taulia and @eugenelesnov (from #124), and @LinuxSuRen (because this fixes a regression of the recently released version 1.5.5)

[efriandika]

I agree with @thomasgl-orange
I found the problem too at my side.. It breaks all of our current pipeline.. :)
Hopefully this PR would be merged shortly :)

[stuartgrieve]

This issue has impacted all of our pipelines too!

[jbdelpech]

Hello, thanks @thomasgl-orange for proposing a fix, I’m sorry to see that my last PR broke your pipelines 🙇‍♂️ . I did not identified your use case.

I made a small feedback.

[thomasgl-orange]

Build failed for infra issues, I will close and reopen the PR to force a rebuild.

[thomasgl-orange]

@efriandika, @stuartgrieve:
An incremental build is available here, if you want to try that rather than downgrading to 1.5.4:
https://repo.jenkins-ci.org/incrementals/io/jenkins/plugins/gitlab-branch-source/1.5.6-rc596.c99e1c847ee7/gitlab-branch-source-1.5.6-rc596.c99e1c847ee7.hpi
(you can upload the .hpi file in the "Advanced" tab of the Update Center)

[efriandika]

Great @thomasgl-orange...
I will try it in next few hours..

Thanks for your works...

[TobiX]

I was affected by this (GitLab on-premise, but proxy needed for internet connection) and this fixed it for me (tested with the incremental)

[cobexer]

Can we expect a speedy release of the updated plugin?

[LinuxSuRen]

LGTM

hi @thomasgl-orange, thanks for your excellent PR.