GitLab MR in Redmine di Doezer

# GitLab MR in Redmine Extension

Prerequisites:
- Merge requests must have the redmine issue ID in the title to be fetched

This extension aims to provide information on the GitLab merge requests associated with a Redmine ticket.

It looks through the user's configured GitLab groups for merge requests with the Redmine issue ID in their title.
Then it displays the merge requests in the issue just before the "Related issues" section. The following information is displayed:
- Source project (not displaying target as I personally don't need it)
- Title
- State
- Title
- Author
- Date of merge (N/A if opened or closed)
- Target branch
- Number of days open

The information is displayed when the page is loaded.
Only trackers of type Task, User Story, Bug, Spike, and Vulnerability are supported to avoid putting unnecessary load on the GitLab host.
Also, only statuses not "new", "product backlog" or "sprint backlog" are checked for the same reason.

To use the extension, you need to input :

- GitLab Host: the URL to your GitLab host, without trailing slash. Default: https://gitlab.com
- GitLab Private Access Token: your private access token taken from GitLab, with the "read_api" permission. Use this link to access the GitLab page.
- Number of days to go back in MR list: for performance reasons, the extension doesn't search for all existing merge requests. Use this field to set the number of days you wish to search back to. Default: 30.
- Select GitLab Groups: click on "Load GitLab Groups", then select the group(s) you want to search merge requests in. A group usually contains multiple repos. It is not currently possible to look in a specific repo.

## Configurable settings :
- Gitlab host
- Gitlab token
- Number of days to go back to when looking for merge requests (for performance reasons)
- Auto fetch enabled or not

## To (try to) do :
- Display Approvers using https://docs.gitlab.com/ee/api/merge_request_approvals.html
- Make configurable the columns displayed for each merge request
- Add unit tests https://railsware.com/blog/test-chrome-extensions/ + chatgpt
- Firefox: ask for permission to access Redmine host? https://blog.mozilla.org/addons/2022/11/17/unified-extensions-button-and-how-to-handle-permissions-in-manifest-v3/

## Changelog
v1.1
- First publication on Mozilla Store

v1.2
- Various fixes

v1.2.0.1
- Added a link to private token page
- Added link when no merge request is found to search for the user to search themselves using the ID
- Added small indication text to the Settings page + make the select required + maybe remove the "group name"
- Allow enabling/disabling automatic retrieval at page load to let the user use the button only