Preserve default total client timeout value

[wombatonfire]

What do these changes do?

Changed default value for ClientTimeout.total so that the default is always present, even if not explicitly specified.

Are there changes in behavior for the user?

If a user wants to adjust some specific client timeout, i.e. connect or sock_connect, they won't need to explicitly specify total timeout value in order to preserve it.

Related issue number

Closes #7274

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes
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[wombatonfire]

Not sure if the documentation should be updated. Currently, it does not describe the behavior that this PR is changing, and the new behavior is somewhat expected, IMHO.

[Dreamsorcerer]

Currently, it does not describe the behavior that this PR is changing

It says it defaults to None:
https://docs.aiohttp.org/en/stable/client_reference.html?highlight=ClientTimeout#clienttimeout

[wombatonfire]

It says it defaults to None:
https://docs.aiohttp.org/en/stable/client_reference.html?highlight=ClientTimeout#clienttimeout

I guess I need glasses :) Updated.

[Dreamsorcerer]

On second thought, is this the expected behaviour if a user were to do something like
ClientTimeout(sock_read=600)?

i.e. They set sock_read to 10 mins, but total is still set to 5 mins, so it achieves nothing.

I'm not sure now if having this default value makes things simpler or more complex...
@webknjaz Any thoughts?