Overview/Summary

Replace this with a brief description of what this Pull Request fixes, changes, etc.

This PR fixes/adds/changes/removes

Replaces CARML modules with AVM
Replaces availability sets with VMSS flex
Introduces scaling plan feature for Personal host pools
New model to get host pool registration token and save it as secret in a keyvault

Replace this with any testing evidence to show that your Pull Request works/fixes as described and planned (include screenshots, if appropriate).

[x] Read the Contribution Guide and ensured this PR is compliant with the guide
[x] Ensured the resource API versions in .bicep file/s I am adding/editing are using the latest API version possible
[x] Checked for duplicate Pull Requests
[x] Associated it with relevant GitHub Issues
[x] (AVD LZA Team Only) Associated it with relevant ADO Items
[x] Ensured my code/branch is up-to-date with the latest changes in the main branch
[x] Performed testing and provided evidence.
[x] Updated relevant and associated documentation (e.g. Contribution Guide, Module READMEs, Docs etc.)