Add the enable tracing opt-in flag

[albertteoh]

Which problem is this PR solving?

Resolves #4680

Description of the changes

• Add an opt-in option --query.enable-tracing to enable tracing for the jaeger-query component.
• The jaeger all-in-one component does not expose this flag since traces are emitted to port 4317 by default, which all-in-one listens on.

How was this change tested?

# Run jaeger-query component with tracing enabled and verify that the connection errors are appearing in stdout.
$ SPAN_STORAGE_TYPE=memory go run -tags ui ./cmd/query/main.go --query.enable-tracing
...
{"level":"info","ts":1692363754.9049716,"caller":"grpc/clientconn.go:1301","msg":"[core][Channel #1 SubChannel #2] Subchannel Connectivity change to CONNECTING","system":"grpc","grpc_log":true}
{"level":"info","ts":1692363754.9050152,"caller":"grpc/clientconn.go:1414","msg":"[core][Channel #1 SubChannel #2] Subchannel picks a new address \"localhost:4317\" to connect","system":"grpc","grpc_log":true}
{"level":"warn","ts":1692363754.9058733,"caller":"grpc/clientconn.go:1476","msg":"[core][Channel #1 SubChannel #2] grpc: addrConn.createTransport failed to connect to {Addr: \"localhost:4317\", ServerName: \"localhost:4317\", }. Err: connection error: desc = \"transport: Error while dialing: dial tcp 127.0.0.1:4317: connect: connection refused\"","system":"grpc","grpc_log":true}
{"level":"info","ts":1692363754.9067123,"caller":"grpc/clientconn.go:1303","msg":"[core][Channel #1 SubChannel #2] Subchannel Connectivity change to TRANSIENT_FAILURE, last error: connection error: desc = \"transport: Error while dialing: dial tcp 127.0.0.1:4317: connect: connection refused\"","system":"grpc","grpc_log":true}
...

# Run jaeger-query component with tracing disabled and verify that the connection errors no longer appear.
# Of course, we can't see traces in Jaeger UI because there's nothing to receive the traces.
$ SPAN_STORAGE_TYPE=memory go run -tags ui ./cmd/query/main.go

# Start an all-in-one instance just as a quick and dirty way to bring up an in-memory jaeger stack to
# receive traces from jaeger-query
$ make run-all-in-one

# Run jaeger-query as a separate component, listening on different ports to all-in-one to avoid port binding collisions.
$ SPAN_STORAGE_TYPE=memory go run -tags ui ./cmd/query/main.go --query.enable-tracing --query.grpc-server.host-port :17685 --query.http-server.host-port :17686 --admin.http.host-port :17687

# Open localhost:17686 in a browser and refresh a few times to emit traces to jaeger all-in-one.

Confirmed that jaeger-query is visible and contains traces:

Checklist

• I have read https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
• I have signed all commits
  - [] I have added unit tests for the new functionality
• I have run lint and test steps successfully
  • for jaeger: make lint test
  • for jaeger-ui: yarn lint and yarn test

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.03% 🎉

Comparison is base (4798446) 97.02% compared to head (615dc07) 97.06%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4685      +/-   ##
==========================================
+ Coverage   97.02%   97.06%   +0.03%     
==========================================
  Files         301      301              
  Lines       17878    17880       +2     
==========================================
+ Hits        17347    17355       +8     
+ Misses        425      421       -4     
+ Partials      106      104       -2     

Flag	Coverage Δ
unittests	97.06% <100.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
cmd/query/app/flags.go	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[albertteoh]

Renamed to jt to avoid clashing names with the jtracer package.

[albertteoh]

Moved here so we just set the global tracer in one place, and removes the otel dependencies from the respective files that use them.

I didn't see, or could think of, a use case where we wouldn't want to set the global tracer when instantiating a jtracer.

Let me know if that's not the case.