feat: added HTTP webhook validation to spin SDK

[Mossaka]

this PR adds the http webhook validation function to Spin SDK; The detailed specification for validation is written here.

This is the first PR to implement the Spin SIP #398 . See related discussion here #394

[lann]

We have been discussing package organization and I think it would make sense for this to live in an outside repository. @michelleN suggests that a new deislabs/spin-cloudevents repo might be a good home for this code plus any future cloudevents trigger executor(s) (which should become much easier with #513!).

Edit: We'll also probably move the redis trigger into a fermyon/spin-redis repo.

[lann]

Oh! We were also discussing adding a "related projects" section to this repo's README, which would include a link to your repo.

[Mossaka]

@lann okay I will try #513 out on a new repo.

[lann]

Is this spec used anywhere apart from CloudEvents?

[Mossaka]

Is this spec used anywhere apart from CloudEvents?

so far I haven't seen it being used in other places.

[radu-matei]

Thanks a lot for the contribution, @Mossaka!

It seems like it would make sense for this functionality to be part of a repo that was focused on adding CloudEvents support for Spin, rather than in the Spin repo itself.
As we were discussing in the developer meeting, that repo could evolve to include support for subscription managers and other things.

Then we can link the repo in the documentation and in the readme.
What do you think?

[Mossaka]

@radu-matei yep I will move to spin-cloudevents repo.