Vale integration [DOC-95]

[JackPGreen]

Make getting started with Vale easier by adding:

• suggested extension for VSCode
• shared config as a submodule
  • note this is currently an internal repo!
• PR builder - e.g. if you look at the diff you can actually see the errors reported on new content only

Out of scope:

• updating the README - adding vale installation and vale sync as a post-checkout step

This is an example of where we could be and probably not a final implementation.

Partially addresses DOC-95

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