Add a pull request check for folder names following the naming convention

[frankieroberto]

We could add a pull request check to make sure that new posts follow the naming convention for folder names (and thus URL structure):

app/name-of-service/YYYY/MM/name-of-post/index.md

where:

• name-of-service matches one of the existing services set up
• YYYY is between 2022 and the current year
• MM is between 01 and 12
• name-of-post is lowercase and hyphen-separated (no spaces or other characters)
• index.md is exactly that

[edwardhorsford]

Should probably only validate folders within a list of named services - we have other pages that don't need to be in dated folders

Things should be lowercase, kebab-cased, with no spaces.