feat(transform): Add Number Minimum Transform

[jshlbrd]

Description

• Adds a new number transform to return the smaller of two values

Motivation and Context

This is a wrapper around Go's math.Min function that works with Substation's data and JSON message formats, and is a peer to #195. If used with number_maximum this allows users to "clamp" numbers between a range, which is added as a config pattern in this PR.

How Has This Been Tested?

Added unit tests and examples.

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.