Publish tracegen

[jpkrohling]

Which problem is this PR solving?

• I'm currently building an autoscaler for Jaeger in the Jaeger Operator. To test that, I could make use of a pod with the tracegen, and the first step is to get a container image built and published somewhere, addressed by this PR.

Short description of the changes

• Added a build step for the trace gen, as well as a Dockerfile
• Changed the docker targets (build/push) to add tracegen
• Allows the tracegen utility to be configured from env

[codecov]

Codecov Report

Merging #2022 into master will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2022      +/-   ##
==========================================
+ Coverage   97.41%   97.43%   +0.01%     
==========================================
  Files         207      207              
  Lines       10243    10243              
==========================================
+ Hits         9978     9980       +2     
+ Misses        223      221       -2     
  Partials       42       42

Impacted Files	Coverage Δ
...lugin/sampling/strategystore/adaptive/processor.go	100% <0%> (+0.79%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update f605a34...c47c275. Read the comment docs.