Add Bicep RPC client library documentation (#18173)

## Description

This pull request adds documentation around using the
`Azure.Bicep.RpcClient` library.

## Example Usage

N/A.

## Checklist

- [x] I have read and adhere to the [contribution
guide](https://github.com/Azure/bicep/blob/main/CONTRIBUTING.md).

###### Microsoft Reviewers: [Open in
CodeFlow](https://microsoft.github.io/open-pr/?codeflow=https://github.com/Azure/bicep/pull/18173)

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Co-authored-by: Bicep Automation <[email protected]>

Author: Gijsreyn