Implement user show restricted features command (ecctl)

@karencfv commented on [Fri Oct 04 2019](https://github.com/elastic/cloud-cli/issues/1022)

## Overview
Now that the swagger spec in `cloud-sdk-go` has been updated to `2.4` there are new endpoints we need to implement.

endpoint ID:
```
get-current-user-restricted-features
```
## Possible Implementation
New command to be implemented:

```console
$ ecctl user show auth-info --current
```
or
```console
$ ecctl user show current-restricted
```

## Testing
All new functions should have their respective unit tests.