[torchx][api] Deprecate Torchx Session Name

[aivanou]

Torchx Runner has a concept of session_name. When user creates a Runner, he/she may provide session_name. If no argument provided, the session_name will be set to: torchx_$user .

This parameter is then used to create a full job name as: session_name-$app_der.name .

The problem is that the default session name torchx_$user is not bound by the max length, and in theory can be very long. This may affect user jobs without them understanding the root cause.

In order to solve this, we can make default session name as torchx_ instead, and omit $user part.

[d4l3k]

It's useful in certain contexts I think. With schedulers where the name is provided in metadata it's not useful but for things like Volcano jobs having that can be beneficial since there's not an easy way to view metadata via vcctl.

However, I don't think that really needs to be on the runner level and could be decided on the scheduler specific level. We don't include the session name or user name currently in the Volcano scheduler so that's a bit of a moot point regardless.

Removing username seems fine, not a big deal, if users want it they can override. If we remove session name entirely might be a bit of a pain point for tracking.

[kurman]

torchx run --scheduler local_cwd --scheduler_args log_dir=/tmp utils.echo --msg "Hello $USER" yields:

...
local_cwd://torchx/echo-mvnppz5dsrkzmc
torchx 2022-05-12 12:51:55 INFO Waiting for the app to finish...
torchx 2022-05-12 12:51:55 INFO Job finished: SUCCEEDED

I believe it was closed in #215

[kiukchung]

lets just add a deprecation warning + docs