Brownfield scenario - Add session hosts to existing host pool

[danycontre]

Overview/Summary

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

This PR fixes/adds/changes/removes

1. New brownfield scenario to add new session hosts to existing host pool (AVD LZA deployment).

Breaking Changes

1. Replace me
2. Replace me

Testing Evidence

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

As part of this Pull Request I have

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

[danycontre]

@swathibhat1 @moisesjgomez @jensheerin add session hosts to existing host pool code merged.