Simplify private class ResteasyClientBuilder

[Puffy1215]

- Renamed private class ResteasyClientBuilder to HttpCredsResteasyClientBuilderImpl to avoid duplicate names and better reflect functionality of class
- Removed getHttpEngine as it holdover from forking from GitLab and their RESTful API version 3

From discussion on #78. Waiting on merge from #78 for fixes.

Investigating the private static class ResteasyClientBuilder inside ResteasyGiteeClientBuilder. Currently, the name matches a now abstract class from Jakarta EE 9 which is un-instantiable. Renaming to HttpCredsResteasyClientBuilderImpl is a more apt name and avoids confusion.

Removed getHttpEngine as it is a holdover from the GitLab fork for this project (17e89c3) to support GitLabs different RESTful api versions (v3 in particular), which is not applicable for Gitee.

Testing done

Tried on Linux Jenkins version 2.504 for via "Test Connection". No issues, successfully connected.

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[MarkEWaite]

Thanks so much for the pull request @Puffy1215 . Are you interested in adopting the plugin? It needs a maintainer, preferably one that is familiar with Gitee and can read and write Chinese. I'm happy to review pull requests and help with maintenance, but I am only confident in English and Italian.

[Puffy1215]

Hi, yes I would love to maintain this! I have created a pull request per the guidelines: jenkins-infra/repository-permissions-updater#4408

I created a message post in the Google mailing list, but I think it needs to be approved.

[MarkEWaite]

I created a message post in the Google mailing list, but I think it needs to be approved.

Developer list message is now visible.

[MarkEWaite]

The changes look good to me, though I'd prefer that you test it interactively as well before merging it. I've labeled it developer so that when it is merged it will generate a new release. If you would prefer to not release it immediately, you can change the label to maintenance or internal.