feat: on demand revalidation route

[okdv]

Description

API route for forcing revalidation of nextjs cache

User must have .env.local setup and it should contain variable REVALIDATION_SECRET, which will be supplied in api call for extra security

Can then revalidate paths with following url (local example)
GET http://localhost:3000/web-map-beta/demo/api/revalidate?secret=TOKEN&path=/top
401 if token is bad
404 if path is bad
500 if error with revalidation function
200 if success

Will add applicable README changes in this PR, once we confirm this is built as desired

Will also add a test for this change, again once confirm its built as desired

Fixes #998 (discovery thread with @dadiorchen )

Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

• Cypress integration
• Cypress component tests

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[okdv]

meant to open as draft, changed it after the fact

[dadiorchen]

Oh, this is amazing, thanks for helping to consider the security problem.

[okdv]

@dadiorchen for sure! I did notice I accidentally am throwing the wrong 4XX errors at some points, will get those updated and set this ready for review

[okdv]

@dadiorchen i think this takes care of the cache revalidation IIRC, i just never finished a small bug and put it out of draft. I'll take care of that

[okdv]

fixed the little bug i mentioned but had forgotten about, submitting for review now

might be a good idea to add a bit into the README about this as well, thoughts on if that is necessary @dadiorchen ?