Use label colors from GitLab issue instead of the hardcoded gray

[oliviergoulet5]

Right now all GitLab labels are rendered in a hardcoded gray color.

It would be better to use the actual label colors returned by the GitLab API so embeds match what users see in GitLab and are easier to visually scan.

Current:

Proposed:

[zthaver]

Please can you assign this to me

[oliviergoulet5]

Thanks for taking this on @zthaver!

You will need to find an endpoint in the GitLab API which returns label colors. However, I haven't actually made sure if one exists yet.

I have been using the following OpenAPI spec to find my way through their API: https://gitlab.com/gitlab-org/gitlab/-/blob/master/doc/api/openapi/openapi_v2.yaml

[oliviergoulet5]

After looking into their API, it seems like you need authorization to view the labels endpoint. E.g. https://gitlab.com/api/v4/projects/gitlab-org%2flanguage-tools%2fgo%2flinters%2flinter2cc/labels

We will need to fallback on the gray labels if the user has no authorization.

Setting this issue as blocked until #16 is resolved.