feat(CLI): adds force-sink flag

[shellcromancer]

Description

This adds a -force-sink flag to the development app to mutate the Sink configuration to a user overridden value. This currently only supports the standard output sink but can be extended to override HTTP, S3 or any sink.

Motivation and Context

When iterating on Substation configs and checking output for pipelines typically destined to a remote output a developer needs to edit the configuration's sink to check results. This change often meant for local testing is an error prone chore which can be automated for this use case via the new -force-sink stdout flag for the development app.

How Has This Been Tested?

I've been using this locally for a few months to save some config while testing.

$ substation -h
...
  -force-sink string
    	force sink output to value (supported: stdout)
...
$ substation -force-sink stdout ...

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[jshlbrd]

updates look good, asked for a change to the GetConfig method but otherwise it's ready to go