Add an inline CSS option to the `as_raw_html` method

[tnederlof]

Prework

• [x] Read and abide by the great_tables code of conduct and contributing guidelines.
• [x] Search for duplicates among the existing issues (both open and closed).

Proposal

Add the ability to inline CSS styles to the `GT.as_raw_html' method to allow tables to render properly in emails.

The gt R packages has a helpful argument inline_css to the as_raw_html() function which inlines CSS styles. This allows tables to render correctly in emails, especially when using this feature in Quarto/Posit Connect (https://docs.posit.co/connect/user/quarto/#email-customization).

[Yasin197]

This would be a great addition! Hope it makes it out on the next release