Support Jaeger tracing configuration

We have recently added support for generating tracing information to GitLab itself: https://docs.gitlab.com/ee/development/distributed_tracing.html

We have yet to add this configuration to Omnibus or our charts however. The Omnibus issue is: gitlab-org/omnibus-gitlab#4104 (closed)

We should add the ability to enable the Jaeger plugin for tracing, along with configuration of the destination Jaeger collector.