Add option not to revoke token on logout

[rominf]

About this change: What it does, why it matters

Keep the current logout behavior by default, but make it possible not to
revoke the token on logout.

$ avn user logout --no-token-revoke

Fix #253.

[dmitrii-vasilev]

LGTM

[edbighead]

Automatically revoking token after logout command is not quite intuitive and can be misinterpreted if not written in big bold red font in documentation.
https://developer.aiven.io/docs/tools/cli/user.html#avn-user-logout

Thinking whether avn user logout --token-revoke is a more user friendly way ?

[rominf]

@edbighead Thanks for your opinion.

Automatically revoking token after logout command is not quite intuitive
Thinking whether avn user logout --token-revoke is a more user friendly way ?

1. I would argue that logout that doesn't invalidate the access token doesn't sound like logout.
2. It's the current behavior, we don't want break current user setups.

if not written in big bold red font in documentation

I agree about the point in the documentation, but I think that the red font and the size are extra. What do you think @aiven/aiven-devrel?

[lornajane]

I am pretty sure our API tooling doesn't support stylesheets. The wording update would be really good to add though!