[Feature Request] All az pipelines variable-group subcommands should support --name argument

**Is your feature request related to a problem? Please describe.**
All `az pipelines variable-group` subcommands should support --name argument.

If user wants to update, show, delete variable groups or add, edit or delete group variabled group-id must be known. To fetch group ip user must do extra manual request with CLI.

**Describe the solution you'd like**
Extension should support --name and fetch group id internally

**Workaround for batch update**
```bash
id=$($CMD pipelines variable-group list $AZ_EXTRA_FLAGS --org "$ORG" --project "$PROJECT" --output tsv --query '[?name == `'common'`]'.id)
$CMD pipelines variable-group delete $AZ_EXTRA_FLAGS --org "$ORG" --project "$PROJECT" --group-id $id
$CMD pipelines variable-group create $AZ_EXTRA_FLAGS --org "$ORG" --project "$PROJECT" --name common --variables $COMMON_VARIABLE_GROUP --authorize true
```