add new custom role assignment for Cosmos Mirroring

[markjbrown]

Description

New bash script creates a custom RBAC role and assignment needed for customers to enable mirroring from cosmos db to fabric. This script is intentionally written to prompt the user for inputs.

Small updates to an existing rbac script

Checklist

• Scripts in this pull request are written for the bash shell.
• This pull request was tested on at least one of the following platforms:
  • Linux
  • Azure Cloud Shell
  • macOS
  • Windows Subsystem for Linux
• The most recent test date and test method are recorded in the script file.
• Scripts do not contain passwords or other secret tokens that are not randomized.
• No deprecated commands or arguments are used. (Release notes)
• All Azure resource identifiers which must be universally unique are guaranteed to be so.
• Resource names use a random function to ensure scripts can be run multiple times in quick succession without error.
• All scripts can be run in their entirely without user input.

Testing information

CLI version:

az --version

Extensions required:

[markjbrown]

#sign-off

[markjbrown]

@dbradish-microsoft hello. Can you merge this PR?

[mikefrobbins]

LGTM