Bugzilla

This patch supports refactoring [AboutWelcome.jsx](https://searchfox.org/mozilla-central/source/browser/components/newtab/content-src/aboutwelcome/aboutwelcome.jsx) to a common component that can replace the [upgrade dialogue](https://searchfox.org/mozilla-central/source/browser/base/content/upgradeDialog.html) and [Spotlight](https://searchfox.org/mozilla-central/source/browser/base/content/spotlight.html) components. 

This work helps set the stage for future patches and should not introduce any changes in UI or existing functionality.

Included work:
 - Drafting a new JSON schema for the AboutWelcome configuration
- Updating AboutWelcome and RTAMO defaults to use the updated configurations 
- Updating AboutWelcome.jsx, MultiStageAboutWelcome.jsx, and MultiStageProtonScreen.jsx to be more configurable and support additional message types

This patch supports refactoring [AboutWelcome.jsx](https://searchfox.org/mozilla-central/source/browser/components/newtab/content-src/aboutwelcome/aboutwelcome.jsx) to a common component that can replace the [upgrade dialogue](https://searchfox.org/mozilla-central/source/browser/base/content/upgradeDialog.html) and [Spotlight](https://searchfox.org/mozilla-central/source/browser/base/content/spotlight.html) components. 

This work helps set the stage for future patches and should not introduce any changes in UI or existing functionality.

Included work:
 - Drafting a new JSON schema for the AboutWelcome configuration
- Updating AboutWelcome and RTAMO defaults to use the updated configurations 
- Updating `AboutWelcome.jsx`, `MultiStageAboutWelcome.jsx`, and `MultiStageProtonScreen.jsx` to be more configurable and support additional message types

This patch supports refactoring [AboutWelcome.jsx](https://searchfox.org/mozilla-central/source/browser/components/newtab/content-src/aboutwelcome/aboutwelcome.jsx) to a common component that can replace the [upgrade dialogue](https://searchfox.org/mozilla-central/source/browser/base/content/upgradeDialog.html) and [Spotlight](https://searchfox.org/mozilla-central/source/browser/base/content/spotlight.html) components. 

This work helps set the stage for future patches and should not introduce any changes in UI or existing functionality.

Included work:
- Drafting a new JSON schema for the AboutWelcome configuration
- Add  `has_noodles` option on configuration and support display of background noodles when this is set to true
- Add support for custom logo url and size
- Support configs with no background_url
- Determine if AboutWelcome's child components are rendered in about:welcome using the window location when conditional logic for that context is required