Merge requests in redmine

# Merge requests in Redmine Extension

**Note: This extension is not associated with GitLab Inc. Currently, only GitLab is supported as a source for merge requests.**

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

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

It looks through the user's configured 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 source 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 :

- Host: the URL to your GitLab host, without trailing slash. Default: https://gitlab.com
- 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 Groups: click on "Load 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 :
- Host URL
- Access token
- Number of days to go back to when looking for merge requests (for performance reasons)
- Auto fetch enabled or not

## Tested with
- Firefox
- Chrome
- Edge
- Redmine 4.1.1
- GitLab Cloud

**Currently supported platforms:** GitLab only

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

v1.2
- Various fixes

v1.2.0.1
- Added link when no merge request is found to let the user search directly on the source platform
- Added indications to the Settings page with a link to the Token page
- Made the "Groups" selection required
- Renamed the "Group name" field to make it more explicit
- Added optional automatic retrieval (auto-fetch) at page load, enabled by default
- Added a small indication under the table that's added to the issue
- Uniformized the name of the extension
- Publication on Chrome Web Store

v1.2.0.2
- Added a check in Agile boards on all "to merge" tickets and its corresponding auto-fetch feature
- Added update pop-up

v1.2.0.3
- Rename extension