Support C# format strings in config

[9swampy]

Description

Support C# format strings in config

Related Issue

Fixes #4156

Motivation and Context

#4156

How Has This Been Tested?

I've implemented a number of formatters and added scenario coverage for implementation but a 4-eyes verification and feedback on appropriateness of scenarios included (or not) would be welcome. The specific scenrio noted on the wish-issue tested here and here.

I've an aversion to Helper classes but that's where I've dropped all this as an extension of the original StringFormatWith but please redirect if it should live elsewhere (or just needs some structure).

Screenshots (if appropriate):

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.