chore: update pull request template, add code review checklist

[themr0c]

chore: updating pull request template

What does this PR do?

• Suggest the usage of a prefix for pull requests titles.
• Distinguish automated and non automated mandatory steps, and in depth review checklist.
• Clarify and complete the review checklist in the pull request template.
• Add a document describing the complete code review checklist.
• Fix language suggestions.

What issues does this PR fix or reference?

The review checklist contains not enough information.

Specify the version of the product this PR applies to

che-docs

Pull Request Checklist for committers and reviewers

The author and the reviewers validate the content of this Pull Request with this checklist, in addition to the automated tests.

• Any procedure:
  • Successfully tested.
  • Describes a scenario already covered by QE tests, otherwise Che QE team has acknowledged an issue.
• Any page or link rename:
  • The page contains a redirection for the previous URL.
  • Propagate the URL change in:
    • Dashboard default branding data
    • Chectl constants.ts
• Builds on Eclipse Che hosted by Red Hat.
• Validate language on files added or modified step reports no vale warnings.

[ibuziuk]

IMO the 28 items checklist split into 3 levels is overkill.
Can we come up with smth simple + automated as much as possible?

Also, let's make a link to workspaces.openshift.com / 'Try it on Eclipse Che hosted by Red Hat ' a requirement for easy verification e.g. - #1986

[themr0c]

Feedback from Che Community call:

• The checklist belongs to the CONTRIBUTING.adoc page.
• Better wording for the "Levels" titles.

[themr0c]

@ibuziuk do you have an example how to write a link to the PR to create in a PR template? It is "easy" to add afterwards when the PR exists, and we have a link, but I don't really see how to achieve that in the template.

[mmorhun]

I completely agree that docs quality should be good, but in my opinion suggested list of requirements is too much and imprecise in some places.
Anyway, thanks to the docs team for working towards better docs and contribution process!

[themr0c]

All suggestions applied. @ibuziuk @pmkovar @mmorhun can you please give a go for another round of reviews?

[rkratky]

@themr0c, nitpick: can we choose between "Pull Request" and "pull request", and only use one? (I vote for the latter.)