feat: support publish docs to readthedocs

[liuxiaocs7]

What type of PR is this?

• [ ] bug
• [ ] feature
• [X] enhancement

What problem(s) does this PR solve?

Issue(s) number:

close: #289

Description:

Hi, @wey-gu, plz help create project plug named nebula-python in readthedocs, and enable this option.

I have tested locally:

• project: https://readthedocs.org/projects/liuxiaocs7-nebula-python/
• website: https://liuxiaocs7-nebula-python.readthedocs.io/en/latest/
• CI is triggered when docs is modified and the bot will add preview website in pr description.(According to https://github.com/readthedocs/actions/tree/v1/preview)

How do you solve it?

Special notes for your reviewer, ex. impact of this fix, design document, etc:

[codecov-commenter]

Codecov Report

All modified lines are covered by tests :white_check_mark:

Comparison is base (cae784f) 77.97% compared to head (0ccb8d7) 77.97%.

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #292 +/- ## ======================================= Coverage 77.97% 77.97% ======================================= Files 18 18 Lines 2415 2415 ======================================= Hits 1883 1883 Misses 532 532 ```

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[wey-gu]

Amazing! Was about to be on a long flight, will apply for it ASAP when I am available!

• [x] work on readthedocs application with community account by @wey-gu

@liuxiaocs7 done with slug nebulagraph-python, I'll PR to adjust that accordingly :)

[Nicole00]

can we just expose the api in module nebula3.gclient? the thrift api is useless for users.

[liuxiaocs7]

can we just expose the api in module nebula3.gclient? the thrift api is useless for users.

Exclude some dirs by EXCLUDE_PATTERNs: https://www.sphinx-doc.org/en/master/man/sphinx-apidoc.html