Add a label parameter when creating pull requests

[Apollo-Roboto]

Describe the solution you'd like
A parameter to add labels to a pull request when creating it with the az repos pr create command.

Example:

az repos pr create \
  --title "A cool pr" \
  --description "With a cool description" \
  --label "documentation"

Additional context
The python module azure-devops is already able to create pull request with labels: Reference 1, Reference 2