Added Hunspell en_US dictionary to Vale configuration

[geoffreynyaga]

This PR integrates the Hunspell en_US dictionary into Vale to enhance spell-checking capabilities.

Changes:

• Added recommended Hunspell en_US dictionary to the Vale configuration. repo

To be advised:

• The styleguide YAML files in styles/Canonical/* have an existing numbering convention. Should we do the same to the en_US_spellcheck.yaml file?
• Test and verify that the dictionary integration works as expected with Vale on CI.

[SecondSkoll]

Actually, could you rename this rule to 000-US-spellcheck.yaml add this rule to vale.ini file in the root with:

Canonical.000-US-spellcheck = error

Just for consistency and so it doesn't run with the style guide check that is currently available.

We'll have to do some testing before this is ready, and it'll be provided with a filter so spelling, terminology, and style checks are all separate.