Install package deps in readthedocs build

[uglide]

Documentation doesn't contain autodoc sections for RediSearch and RedisJson modules:

The root cause is

WARNING: autodoc: failed to import module 'search.commands' from module 'redis.commands'; the following exception was raised:
No module named 'async_timeout'

from https://readthedocs.org/api/v2/build/18595317.txt

Pull Request check-list

Please make sure to review and check all of these items:

• Does $ tox pass with this change (including linting)?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)?
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

NOTE: these things are not required to open a PR and can be done
afterwards / while the PR is open.

Description of change

Please provide a description of the change here.

[codecov-commenter]

Codecov Report

Base: 92.20% // Head: 92.20% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (75a2611) compared to base (e425674).
Patch has no changes to coverable lines.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2465   +/-   ##
=======================================
  Coverage   92.20%   92.20%           
=======================================
  Files         113      113           
  Lines       29239    29239           
=======================================
+ Hits        26959    26961    +2     
+ Misses       2280     2278    -2     

Impacted Files	Coverage Δ
tests/test_asyncio/test_search.py	98.26% <0.00%> (-0.35%)	⬇️
tests/test_cluster.py	96.97% <0.00%> (+0.22%)	⬆️

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