'envoy --version' should provide actual version, ex: 1.5.0

*Title*: 'envoy --version' should provide actual version, ex: 1.5.0

*Description*:
currently 'envoy --version' provides you with an SHA which is not much useful for end users. I would expect to see a version such as "1.5.0" there.

Something like:
```
envoy --version
version: 1.5.0
tag: a8507f67225cdd912712971bf72d41f219eb74ed/Modified/RELEASE
```

