Proposal: Bicep CLI commands for Azure operations

The reasons why I think this is beneficial are:
* Reduces duplication in CI pipelines, and simplifies local reproducability.
* Gives the Bicep author more control over exposing configuration.
* Permits better validation during authoring, and a more coherent validation experience when deploying.
* Works well with other proposed commands such as `bicep what-if` and `bicep destroy`.

## Goals

### Main Goals
* Propose a set of `.bicepparam` syntax changes and new Bicep CLI command groups for managing deployments.
* Propose an approach on rationalizing some of the more recent language features against each other (extension configs, external inputs), along with other proposed features such as `bicep deploy`.
* Propose improvements to visualization of deployments.

### Other Goals
* Simplify migration from deployments to deployment stacks.
* Provide higher-quality visualization for errors, diagnostics, and real-time operations.

## New Syntax

The syntax proposals are all changes to the `.bicepparam` file syntax.

### Changes to `using`

Rather than relying on CLI arguments for configuration, configuration can be specified using a `with` clause:

```bicep
using 'main.bicep' with {
mode: 'deployment'
scope: resourceGroup('f794b1c4-c575-4f8d-9eb0-1816c630c110', 'myRg')
name: 'main' // optional
}

param foo = 'bar'
```

For Deployment Stacks:
```bicep
using 'main.bicep' with {
mode: 'stack'
scope: resourceGroup('f794b1c4-c575-4f8d-9eb0-1816c630c110', 'myRg')
name: 'myStack'
actionOnUnmanage: {
resources: 'delete'
}
denySettings: {
mode: 'denyDelete'
}
}

param foo = 'bar'
```

CLI usage:
```sh
bicep what-if main.bicepparam
bicep deploy main.bicepparam
# if using stacks
bicep destroy main.bicepparam
```

### New `readEnvVar()` & `readCliArg()` functions

Use the new `externalInput()` function as a way of giving the author control over how run-time values are read.

Define `readCliArg()` and `readEnvVar()` as syntactic sugar for `externalInput`:
* `readCliArg()` would be syntactic sugar for `externalInput('sys.cliArg', )`
* `readEnvVar()` would be syntactic sugar for `externalInput('sys.envVar', )`

* Example usage for `readEnvVar`:
```bicep
var subscriptionId = readEnvVar('AZURE_SUBSCRIPTION_ID')

using 'main.bicep' with {
mode: 'deployment'
scope: resourceGroup(subscriptionId, 'myRg')
}
```

CLI experience:
```sh
export AZURE_SUBSCRIPTION_ID=f794b1c4-c575-4f8d-9eb0-1816c630c110
bicep what-if main.bicepparam
bicep deploy main.bicepparam
```
* Example usage for `readCliArg`:
```bicep
var subscriptionId = readCliArg('subscription-id')

using 'main.bicep' with {
mode: 'deployment'
scope: resourceGroup(subscriptionId, 'myRg')
}
```

CLI experience:
```sh
bicep what-if --arg-subscription-id f794b1c4-c575-4f8d-9eb0-1816c630c110 main.bicepparam
bicep deploy --arg-subscription-id f794b1c4-c575-4f8d-9eb0-1816c630c110 main.bicepparam
```

These functions would be valid anywhere in the param file - not just in the `scope` field. For example:
```bicep
using 'main.bicep' with {
mode: 'deployment'
scope: resourceGroup('f794b1c4-c575-4f8d-9eb0-1816c630c110', 'myRg')
}

type EnvironmentType = 'test' | 'prod'

var environment EnvironmentType = readCliArg('env-name')

var config = {
test: ...
prod: ...
}[environment]

param envSuffix = config.suffix
```

Usage:
```sh
bicep deploy --arg-env-name test
bicep deploy --arg-env-name prod
```

## New CLI Commands

### `bicep deploy`

Initiates a deployment to Azure.

Provides a clean interface for tracking operations in real time and visualizing failures:

### `bicep what-if`

Runs a what-if on Azure and reports results. Can also be used for validation only without returning results.

### `bicep destroy`

Deletes a Deployment Stack. Only valid if the `.bicepparam` file has been configured as a Stack with the `mode` property.

## Changes to existing CLI Commands

### `bicep local-deploy`

Remove this command group entirely, and just have "Local" be available under the `bicep deploy` command.

### `bicep snapshot`

Align with the arguments proposed for the new CLI command groups (`bicep deploy` etc).

## Other notes
### Deploy Pane
If accepted, the Deployment pane should be updated to operate with this new form of configuration.

## Trying this out

This functionality is currently available on an experimental branch. See [here](https://github.com/Azure/bicep/blob/ant/poc_cli/deploy/README.md) for information on previewing it.

https://github.com/user-attachments/assets/da64f3a3-3c11-411b-94b6-6324f79af107