Add option to set base path in upstream Jaeger chart

In order for us to offer reverse proxy support for Jaeger, we will need to support setting its base path. Otherwise we will need to implement a significant amount of re-writing support for URL's as it transits GitLab, which is non-trivial.

Unfortunately the chart does not expose these options yet. Rather than forking the chart, we should submit an upstream PR to add this.

Configuration flag 'queryBasePath`: https://github.com/jaegertracing/jaeger/blob/master/cmd/query/app/flags.go#L47