Change old wiki link to docs.codabench.org links

[ObadaS]

A brief description of the purpose of the changes contained in this PR.

Change old wiki link to docs.codabench.org links

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

[ObadaS]

While making the changes, I noticed that we have a help button that doesn't have any wiki/documentation pages associated to it

This leads to https://github.com/codalab/codabench/wiki/Task-&-Dataset-Management which is empty

[ihsaan-ullah]

@ObadaS I have mode some small changes in my last commit, mostly changing the word wiki to docs in multiple files.

Some comments that we may want to consider and update in another PR:

1. At multiple places we have %3A in some urls. We should remove this
2. We have Governance, privacy policy and About still in the old wiki. We may want to move them to dedicated pages like CONTRIBUTING.md. After that we should change the links too everywhere
3. We have two folders for docs: documentation and docs. We should check docs and move it to documentation or remove it.

I let you decide about these points. And you can merge the PR.

[ObadaS]

I will merge this for now and keep the other points in mind so that we can fix them in a future PR.
Thanks for the review and the changes, I forgot that we had a lot of "wiki" that had to be changed to "docs" now.

As for the docs folder, it's definitely something we need to do. The content doesn't seem to be interesting anymore. I'll import the things we might need and discard the rest

[ihsaan-ullah]

Perfect. I have noted these points in an issue here (#2083) so that we don't forget