Clientsession timeout property

[ghost]

What do these changes do?

Added ClientSession.timeout property.

Are there changes in behavior for the user?

To get the timeout of the session user would use session.timeout instead of session._timeout.

Related issue number

Fixes #4191

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
• If you provide code modification, please add yourself to CONTRIBUTORS.txt
  • The format is <Name> <Surname>.
  • Please keep alphabetical order, the file is sorted by names.
• Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> for example (588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the pr
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: "Fix issue with non-ascii contents in doctest text files."

[codecov-io]

Codecov Report

Merging #4193 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4193      +/-   ##
==========================================
- Coverage   97.57%   97.56%   -0.02%     
==========================================
  Files          43       43              
  Lines        8825     8825              
  Branches     1381     1381              
==========================================
- Hits         8611     8610       -1     
- Misses         92       93       +1     
  Partials      122      122

Impacted Files	Coverage Δ
aiohttp/web_fileresponse.py	97.72% <0%> (-0.57%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 6236536...2f0d3e3. Read the comment docs.

[asvetlov]

Awesome!