fix: otel http parent propogation

[markphelps]

Fixes issue raised in the community forum: https://community.flipt.io/t/ofrep-http-trace-context-propagation/66

It seems GRPC gateway / OTEL grpc instrumentation does not properly proxy the traceparent information via HTTP headers if present. This fixes that.

It also removes a couple deprecated method calls/setup from the OTEL/grpc projects

See: openfga/openfga#1624

Note: I used stdoutracing for demonstrating the changes before/after
Note: This also adds a new span named grpc-gateway before the grpc gateway span (ie: flipt.ofrep.OFREPService/EvaluateFlag)

Here's an example request, note the traceparent header which is used for parent span propagation:

curl --request POST \
  --url http://localhost:8080/ofrep/v1/evaluate/flags/adsfasd \
  --header 'content-type: application/json' \
  --header 'traceparent: 00-0af7651916cd43dd8448eb211c80319c-00f067aa0ba902b7-01' \
  --data '{
  "targetingKey":"foo"
}'

Before

Parent span is 000...

{
	"Name": "flipt.ofrep.OFREPService/EvaluateFlag",
	"SpanContext": {
		"TraceID": "570bf9d8a8b7c963664070d928e32a0a",
		"SpanID": "e4ab9f0a37167da9",
		"TraceFlags": "01",
		"TraceState": "",
		"Remote": false
	},
	"Parent": {
		"TraceID": "00000000000000000000000000000000",
		"SpanID": "0000000000000000",
		"TraceFlags": "00",
		"TraceState": "",
		"Remote": true
	},

After

Parent span is set correctly and traces are linked

{
	"Name": "flipt.ofrep.OFREPService/EvaluateFlag",
	"SpanContext": {
		"TraceID": "0af7651916cd43dd8448eb211c80319c",
		"SpanID": "6ec222e7bc6ad1f9",
		"TraceFlags": "01",
		"TraceState": "",
		"Remote": false
	},
	"Parent": {
		"TraceID": "0af7651916cd43dd8448eb211c80319c",
		"SpanID": "c4c833244fa22146",
		"TraceFlags": "01",
		"TraceState": "",
		"Remote": false
	},
	...
}
{
	"Name": "grpc-gateway",
	"SpanContext": {
		"TraceID": "0af7651916cd43dd8448eb211c80319c",
		"SpanID": "c4c833244fa22146",
		"TraceFlags": "01",
		"TraceState": "",
		"Remote": false
	},
	"Parent": {
		"TraceID": "0af7651916cd43dd8448eb211c80319c",
		"SpanID": "00f067aa0ba902b7",
		"TraceFlags": "01",
		"TraceState": "",
		"Remote": true
	},
	....
}

[codecov]

Codecov Report

Attention: Patch coverage is 12.50000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 64.61%. Comparing base (7cb00e0) to head (119867a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/cmd/http.go	0.00%	4 Missing ⚠️
cmd/flipt/main.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3758      +/-   ##
==========================================
- Coverage   64.63%   64.61%   -0.03%     
==========================================
  Files         170      170              
  Lines       17233    17241       +8     
==========================================
+ Hits        11139    11140       +1     
- Misses       5399     5406       +7     
  Partials      695      695              

Flag	Coverage Δ
unittests	64.61% <12.50%> (-0.03%)	⬇️

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[erka]

niiice