fix(api): bug bash preview issues resolved

[tatarco]

What changed? Why was the change needed?

During the bug bash the preview endpoint appeared to be very fragile, attempt to make it more robust was difficult due to the structure of the use cases, multiple linear bugs resolved + a massive cleanup and alignment to consistent company standards
what was done?

1. Pipe {{ttt | upper}} not converting to payload correctly.
   2.. {{}} failing preview
   3.. Variable validation agains Available Variable schema (validate {{name}} illegal.
   4.. Control values sanitation on preview ( illegal placeholders will be removed for preview but persisted along with errors in the DB to keep the UX consistent
   5.. computed Payload schema is now persisted (as string ) on upsert and served from the DB on get test data

Screenshots

Expand for optional sections

Related enterprise PR

Special notes for your reviewer

[netlify]

✅ Deploy Preview for novu-stg-vite-dashboard-poc ready!

Name	Link
🔨 Latest commit	2de6c77
🔍 Latest deploy log	https://app.netlify.com/sites/novu-stg-vite-dashboard-poc/deploys/6735ed866fc9e20008cb9981
😎 Deploy Preview	https://deploy-preview-6904--novu-stg-vite-dashboard-poc.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site configuration.

[pkg-pr-new]

Open in Stackblitz

@novu/client

pnpm add https://pkg.pr.new/novuhq/novu/@novu/client@6904

@novu/framework

pnpm add https://pkg.pr.new/novuhq/novu/@novu/framework@6904

@novu/headless

pnpm add https://pkg.pr.new/novuhq/novu/@novu/headless@6904

@novu/js

pnpm add https://pkg.pr.new/novuhq/novu/@novu/js@6904

@novu/nest

pnpm add https://pkg.pr.new/novuhq/novu/@novu/nest@6904

@novu/nextjs

pnpm add https://pkg.pr.new/novuhq/novu/@novu/nextjs@6904

@novu/node

pnpm add https://pkg.pr.new/novuhq/novu/@novu/node@6904

@novu/notification-center

pnpm add https://pkg.pr.new/novuhq/novu/@novu/notification-center@6904

novu

pnpm add https://pkg.pr.new/novuhq/novu@6904

@novu/providers

pnpm add https://pkg.pr.new/novuhq/novu/@novu/providers@6904

@novu/react

pnpm add https://pkg.pr.new/novuhq/novu/@novu/react@6904

@novu/react-native

pnpm add https://pkg.pr.new/novuhq/novu/@novu/react-native@6904

@novu/shared

pnpm add https://pkg.pr.new/novuhq/novu/@novu/shared@6904

@novu/stateless

pnpm add https://pkg.pr.new/novuhq/novu/@novu/stateless@6904

commit: 2de6c77