[Feature Request] service-endpoint create support to read from stdin

Creating a service connection to an arbitrary service (such as Docker Hub) with:

```
az devops service-endpoint create --service-endpoint-configuration foo.json
```

requires the use of `--service-endpoint-configuration` to read from a JSON-encoded file containing the POST request to be sent. But in a CI environment this will typically require first creating a (hopefully temporary) file with cleartext credentials which is not desirable. On UNIX system you can work around this with:

```
sed -e 's/MY_PASSWORD_TOKEN/MY_ACTUAL_PASSWORD/' foo.json | az devops service end-point create --service-endpoint-configuration /dev/stdin
```

but I'm not sure how you would do this on Windows? It would be useful if there was an alternate parameter named something like `--service-endpoint-configuration-from-stdin` that would explicitly support reading the required JSON snippet from stdin in a cross platform way.