Unclear docs and error message for --match-conditions format

**Related command**

```
az network application-gateway waf-policy custom-rule create \
--resource-group my-group \
--policy-name my-policy \
--name azuredevopsip \
--priority 10 \
--rule-type MatchRule \
--match-conditions '[{"variables": "RemoteAddr","operator":"IPMatch","values": ["'"$CURRENT_IP"'"]}]' \
--action Allow
```

**Is your feature request related to a problem? Please describe.**
When reading docs / looking at examples, I was not able to find any relevant information about how `--match-conditions` should be formatted.

When I ran this command I got the error `Failed to parse '--match-conditions' argument: Model 'AAZObjectArg' has no field named 'RemoteAddr'`

When running `--match-conditions` with `??` for docs it suggested `variables [Required] Space-separated list of variables to use when matching. Variable values: RemoteAddr, RequestMethod, QueryString, PostArgs, RequestUri, RequestHeaders, RequestBody, RequestCookies. Try "??" to show more.`.

Documentation on [azure-cli docs](https://learn.microsoft.com/en-us/cli/azure/network/application-gateway/waf-policy/custom-rule?view=azure-cli-latest) doesn't present any examples on `--match-conditions`.

Solution to this was to pass variables as an array of objects, where each key should have one of the values from `RemoteAddr, RequestMethod, QueryString, PostArgs, RequestUri, RequestHeaders, RequestBody, RequestCookie`.

Correct format:
```
--match-conditions '[{"variables":[{"variableName":"RemoteAddr"}],"operator":"IPMatch","values": ["'"$CURRENT_IP"'"]}]'
```

**Describe the solution you'd like**
The error message returned did not describe clear enough what the problem was, it suggested the variables key was not correct, but the docs referred to that it should be one of the `RemoteAddr, RequestMethod, QueryString, PostArgs, RequestUri, RequestHeaders, RequestBody, RequestCookie`.

**Describe alternatives you've considered**
Including example payloads of --match-conditions.

**Additional context**