Allow declaration of deployment name in bicep file

**Is your feature request related to a problem? Please describe.**
I guess it's a common thing that people name their main bicep file `main.bicep` cause this is how you can find the entrypoint if there is multiple files.
By default the `Microsoft.Resources/deployments` will be named after the filename `main`.
In automation scenarios this bears the risk for concurrent deployments to interfere with each other resulting in undefined behavior.
> For the details take a look here: https://learn.microsoft.com/en-us/azure/azure-resource-manager/bicep/deploy-powershell#deployment-name
> Start reading from _If you run concurrent deployments ..._
> To me this almost sounds like someone making a bad joke :D

Yes it is possible to declare a deployment name as a commandline option.
However in my use-case I as a template author would like to define the deployment name inside the bicep file.
This would allow me to ship better quality templates as chances for conflicts is lower and consumers don't have to specify the deployment name as a commandline option.

**Describe the solution you'd like**
Add new keyword `deploymentName` to declare deployment name in bicep file.
A deployment name specified as commandline option should take precedence.

```bicep
targetScope = 'subscription'

var version = '7.1.0'

deploymentName = 'myproduct_${version}'

...
```

Start with the main.bicep example and the deployment-name command-line option described in the issue. Define how a deploymentName declaration should work, including command-line precedence, and verify that the requested syntax supports the targetScope example.

Written by the indexing model from the issue text.