Move remoting3's UserAgent here

[ash211]

https://github.com/palantir/http-remoting/blob/develop/http-clients/src/main/java/com/palantir/remoting3/clients/UserAgent.java

[ash211]

@uschi2000 @j-baker this is important for an internal library that needs to accept UserAgents as part of its API. I'd prefer for that to be an object in http-remoting-api than in remoting3.

Are we able to move remoting3's UserAgent into remoting-api without requiring a bump to remoting4?

[uschi2000]

Don't think we can move it without going to remoting4.

[ash211]

Ok I'll use name/version for now, and just do another API major version break in foundry-spark when we go to remoting-api.UserAgent