fwutil update all incorrectly autocompletes to fwutil update auto

[alexrallen]

Description

The click library uses the names of functions to assist in the generation of CLI auto-complete trees. In fwutil update the method for updating all available firmware is auto_update

See here: https://github.com/Azure/sonic-utilities/blob/1029c5487dd1190215dae6ca557d6feb96113c9d/fwutil/main.py#L406

# 'auto_update' group
@click.group()
@click.pass_context
def auto_update(ctx):
    """Auto-update platform firmware"""
    pass

This is causing click to mistakenly label the command as auto instead of all as defined lower in the file. Renaming this function to all_update resolves this problem.

Steps to reproduce the issue:

1. Type fwutil update
2. Hit tab

Describe the results you received:

root@r-qa-sw-eth-21101:/home/admin# fwutil update 
auto     chassis  module  

Describe the results you expected:

root@r-qa-sw-eth-21101:/home/admin# fwutil update 
all    chassis  module  

[dgsudharsan]

@sujinmkang FYI