Make PFC commands use a class

[bktsim-arista]

What I did

This change puts contents originally in pfc/main.py into a class, to support the usage of the multi-asic helper in a future change. This change is required, as multi-asic helper being used expects members self.config_db and self.db to exist when a function with the decorator run_on_multi_asic is called. The multi-asic class helper will be used to add multi-asic support to pfc commands in a following pull request.

This is a part of the set of changes being pushed for https://github.com/sonic-net/sonic-buildimage/issues/15148

How I did it

Moved contents of PFC commands into a class. There are no functional changes.

[arista-nwolfe]

/azpw run Azure.sonic-utilities

[wenyiz2021]

/azpw run

[arlakshm]

/azpw run Azure.sonic-utilities

[arlakshm]

/azp run Azure.sonic-utilities

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).

[vmittal-msft]

/azp run

[azure-pipelines[bot]]

Azure Pipelines successfully started running 1 pipeline(s).

[kenneth-arista]

Because of the conversion of global methods to class methods, there are lots of white space changes. The best way to review this PR is to ignore whitespace.

[bingwang-ms]

@bktsim-arista Please file a direct PR to 202405 branch to address the conflict.

[kenneth-arista]

@bktsim-arista Please file a direct PR to 202405 branch to address the conflict.

There's no need to cherry-pick this PR into 202405 because commit 64473080 is already included. 😄 Can you change the label to already included in 202405?