[INF] Set independent environment for building documentation

[Zeroto521]

PR Description

Please describe the changes proposed in the pull request:

/environment-dev.yml is complex.
It's used for building doc, setting developer local env, and setting ci test env.
This file becomes big and big and hard to understand.

Part of #1133.

PR Checklist

Please ensure that you have done the following:

1. PR in from a fork off your branch. Do not PR from <your_username>:dev, but rather from <your_username>:<feature-branch_name>.

2. If you're not on the contributors list, add yourself to AUTHORS.md.

3. Add a line to CHANGELOG.md under the latest version header (i.e. the one that is "on deck") describing the contribution.
   • Do use some discretion here; if there are multiple PRs that are related, keep them in a single line.

Automatic checks

There will be automatic checks run on the PR. These include:

• Building a preview of the docs on Netlify
• Automatically linting the code
• Making sure the code is documented
• Making sure that all tests are passed
• Making sure that code coverage doesn't go down.

Relevant Reviewers

Please tag maintainers to review.

• @ericmjl

[Zeroto521]

The value of channels and activate-environment use the variable of mkdocs/environment.yml

[Zeroto521]

default will activate that env

[codecov]

Codecov Report

Merging #1141 (933bcf8) into dev (f753323) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #1141   +/-   ##
=======================================
  Coverage   97.34%   97.34%           
=======================================
  Files          77       77           
  Lines        3240     3240           
=======================================
  Hits         3154     3154           
  Misses         86       86           

[ericmjl]

Only one change request, and then let's merge!

[Zeroto521]

Why this test case (tests/functions/test_conditional_join.py::test_multiple_eqs_extension_array) failed in https://github.com/pyjanitor-devs/pyjanitor/runs/7761821318?check_suite_focus=true but passed now?

[ericmjl]

Why this test case (tests/functions/test_conditional_join.py::test_multiple_eqs_extension_array) failed in https://github.com/pyjanitor-devs/pyjanitor/runs/7761821318?check_suite_focus=true but passed now?

I'm not sure, @Zeroto521 - some tests may be flaky, I guess. Usually a re-run of the CI might do the trick.

With everything green, I'm happy to merge!