keep http params sigstore java user-agent up to date.

[bobcallaway]

Description

It would be good for clients to be able to specify a User-Agent header on HTTP requests to sigstore services.

@loosebazooka

[loosebazooka]

this is already possible using httpParams: https://github.com/sigstore/sigstore-java/blob/main/sigstore-java/src/main/java/dev/sigstore/http/HttpParams.java

However we don't inject the version into there which is probably something we should do. @vlsi any ideas for injecting compile time vars (rather than reading the jar manifest?)

[vlsi]

WDYT of generating a class with the compile-time constants?

[vlsi]

I can replicate something like https://github.com/pgjdbc/pgjdbc/blob/master/pgjdbc/src/main/version/org/postgresql/util/DriverInfo.java

[loosebazooka]

Yeah, lets do that. Let me know if you want someone else to pick it up. I can also do it.