Add webhooks intro page + changes for challenge enhancement

[shikhartanwar]

Description

This PR makes the following changes:

• Adds webhook intro page which was missed during migration it seems
• Refactors runtime webhooks as another page (webhooks intro is the index page now)
• Adds documentation for asynchronous validation for new challenge workflow

How Has This Been Tested?

npm run dev gives the following error so this could not be tested locally as mentioned in the README.md. This error comes in the main branch as well.
However, I have made sure that the markdown preview and links are correct.

Screenshots (if appropriate):

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[icaraps]

These pages were moved in app-builder docs see AdobeDocs/app-builder#136
cc @sarahxxu @kgera to clarify

[icaraps]

npm run dev gives the following error

Which node version are you using ? Please use v14.x (LTS) which supports optional chaining.

[shikhartanwar]

These pages were moved in app-builder docs see AdobeDocs/project-firefly#136 cc @sarahxxu @kgera to clarify

IMHO, intro to webhooks is a critical page for events documentation as well. So, ideally it should coexist in both repositories unless I am missing some context here.

[shikhartanwar]

npm run dev gives the following error

Which node version are you using ? Please use v14.x (LTS) which supports optional chaining.

v12.18.3. Will try with 14.x.
@icaraps: Shall we add this info in the README.md as well?

[icaraps]

@shikhartanwar the readme mentions Node.js LTS as prerequisite https://github.com/adobe/aio-theme#getting-started

[shikhartanwar]

@shikhartanwar the readme mentions Node.js LTS as prerequisite https://github.com/adobe/aio-theme#getting-started

Thank you @icaraps. Changing to Node v14.x worked.

Quick question: Is it possible to have another level of indentation for the side bar on the right?

[kgera]

I see we haven't changed branding from I/O to IO anywhere. So, lets continue the same way. Rest all good.

[icaraps]

@shikhartanwar

Is it possible to have another level of indentation for the side bar on the right?

No it's currently max 2 levels only per design.