feat: Add support for using existing Fabric capacity during deployment

[Saswato-Microsoft]

• Introduced 'deployFabricCapacity' parameter to control fabric capacity deployment.
• Added 'existingFabricCapacityName' parameter for specifying existing fabric capacity name.

Purpose

This pull request introduces support for using an existing Fabric capacity during deployment, rather than always creating a new one. It adds new parameters to control this behavior, updates the deployment logic, and improves documentation to guide users through the new options.

Deployment parameterization and logic:

• Added new parameters deployFabricCapacity (boolean) and existingFabricCapacityName (string) to infra/main.bicep to allow selection between deploying a new Fabric capacity or using an existing one.
• Updated the deployment logic in infra/main.bicep to conditionally create a Fabric capacity module only if deployFabricCapacity is true, and to resolve the output capacity name appropriately. [1] [2]
• Updated infra/main.parameters.json to include the new parameters, allowing them to be set via environment variables.

Documentation updates:

• Improved the deployment guide in docs/DeploymentGuide.md with instructions and notes on how to use an existing Fabric capacity by setting the relevant environment variables.

Does this introduce a breaking change?

• Yes
• No

How to Test

• Get the code

git clone [repo-address]
cd [repo-name]
git checkout [branch-name]

• Test the code

What to Check

Verify that the following are valid

• ...

Other Information