[Feature][gitlab] API to list all `projects` for gitlab

[klesh]

Search before asking

• I had searched in the issues and found no similar feature requirement.

Description

In order to support #2271. We need a new API

Solution

Add API GET /api/proxy/gitlab/projects?keyword=&page=2&size=10, searching and pagination are critical since the total number of projects is likely to be huge.

Use case

To support #2271

Related issues

#2271

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[warren830]

I checked gitlab api: https://docs.gitlab.com/ee/api/projects.html#list-user-projects
we can use the following param:
search(string): Return list of projects matching the search criteria.
starred(boolean): Limit by projects starred by the current user.
visibility(string): Limit by visibility public, internal, or private. -- using private will return only our company's private projects

[warren830]

according to #2705 , I added a proxy to allow config-ui to request gitlab projects
from config-ui, we can easily send the following request:
http://localhost:4000/api/plugins/gitlab/connections/:connectionId/proxy/rest/projects?visibility=private
Then we will get the response as below:

[
	{
		"id": *****,
		"description": "用于auto-test的自己的CI方面的测试",
		"name": "demo-auto-test"
	}
]