Attempt to fix readthedocs build

[daico007]

PR Summary:

For some reason, the docs build on PR has been failing (for a while). This PR will attempt to find and fix that issue.

PR Checklist

---

• [ ] Includes appropriate unit test(s)
• [ ] Appropriate docstring(s) are added/updated
• [ ] Code is (approximately) PEP8 compliant
• [ ] Issue(s) raised/addressed?

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: -1.87 :warning:

Comparison is base (d1c1f33) 86.89% compared to head (fe7965e) 85.02%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1105 +/- ## ========================================== - Coverage 86.89% 85.02% -1.87% ========================================== Files 61 61 Lines 6318 6319 +1 ========================================== - Hits 5490 5373 -117 - Misses 828 946 +118 ``` | [Impacted Files](https://app.codecov.io/gh/mosdef-hub/mbuild/pull/1105?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mosdef-hub) | Coverage Δ | | |---|---|---| | [mbuild/recipes/\_\_init\_\_.py](https://app.codecov.io/gh/mosdef-hub/mbuild/pull/1105?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mosdef-hub#diff-bWJ1aWxkL3JlY2lwZXMvX19pbml0X18ucHk=) | `100.00% <100.00%> (ø)` | | | [mbuild/utils/io.py](https://app.codecov.io/gh/mosdef-hub/mbuild/pull/1105?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mosdef-hub#diff-bWJ1aWxkL3V0aWxzL2lvLnB5) | `83.62% <100.00%> (ø)` | | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/mosdef-hub/mbuild/pull/1105/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mosdef-hub)

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[daico007]

Ok, I think the docs (somehow) is building correctly now. There were a combinatotiral issue with the fail_on_warning clause in .readthedocs.yml compounded with some deprecated warnings, missing dependencies, etc. But I hand checked the built docs and all pages seems to be built alright (especially those writers which are built from their docstrings). So, I think this PR is ready for review, if you want to have a look at it @chrisiacovella, if not I can merge it either tomorrow or wednesday.

Also, we have an DeprecatedWarnings regading the pkg_resrouces, which is currently used in mbuild/utils/io.py and mbuild/recipes/__init__.py that we might also want to take care of. I will try to poke a round and see what's the updated syntax should be and push it in later.