Leaderboard always visible

[Didayolo]

Possible reviewer: @ihsaan-ullah

Description

The goal of this PR is to have always the leaderboard results publicly visible for all public competitions, even when the user is not logged in or not part of the competition:

We could also make this an option, but I am in favor of this policy of having it always visible, as it is the case in CodaLab and in Kaggle. This way we encourage transparency of benchmark results, and help works that refer Codabench competitions and benchmarks.
--> We validated that we want it this way, so it's all fine with this PR.

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The following changes in api/serializers/leaderboards.py may also generally improve the way we fetch leaderboard and order the submission:

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The PR also include a minor UI improvement:

Issues this PR resolves

• closes Public Leaderboard for Competition #1848

A checklist for hand testing

Check the "Leaderboard" and the "Submission" tabs when:

• Not logged in
• Not participating
• Denied
• Participating
• Being admin
• When there are leaderboard submissions or not

Checklist

• Code review by me
• Hand tested by me
• I'm proud of my work
• Code review by reviewer
• Hand tested by reviewer
• CircleCi tests are passing
• Ready to merge

[ihsaan-ullah]

I am facing some issues in testing this PR (not related to this PR). Issue reported here: #2003

[ihsaan-ullah]

Test

Competition is public

• User not logged in -> Leaderboard: shows all leaderboard submissions, Submission Panel: Yellow message with terms and Login/SignUp options
• User logged in but not a participant -> Leaderboard: shows all leaderboard submissions, Submission Panel: Yellow message with terms and Register option
• User logged in but waiting for participation -> Leaderboard: shows all leaderboard submissions, Submission Panel: Yellow message saying that admin will approve your request
• User logged in but denied participation -> Leaderboard: shows all leaderboard submissions, Submission Panel: Red message saying that your request is denied
• User logged in and approved participation -> Leaderboard: shows all leaderboard submissions, Submission Panel: shows normal submission panel view
• User is admin: user can see both submission panel and leaderboard

NOTE

We should add as a feature an option to hide leaderboard from non participant users.

[Didayolo]

We should add as a feature an option to hide leaderboard from non participant users.

I think we discussed that and decided it was not necessary