Add E2E test for exemplars API

[yeya24]

Now the exemplars API is added and we already instrumented Thanos with exemplars in #3977. It is time to add an E2E test case for it.

AC:
1. Add a Jaeger all in one service in the E2E test as it is required for tracing
2. Update the options to start Thanos component with tracing configs
3. Call the exemplars API from thanos querier and check the results

For the request and response of the exemplars API, please check https://prometheus.io/docs/prometheus/latest/querying/api/#querying-exemplars

[yeya24]

This test case itself should be easy to implement. However, we might be blocked by another test case TestRulesAPI_Fanout.
This is mentioned https://github.com/thanos-io/thanos/pull/3905/files#r591791448.
The latest version Prometheus has strict unmarshalling so we need to fix this test case first.

[yeya24]

Assign this to myself.