refactor: use OTel autoprop package

[pellared]

Refactor to use https://pkg.go.dev/go.opentelemetry.io/contrib/propagators/autoprop

The refactoring is nicely tested by the following existing tests:

$ go test -v -run TestConfig/Propagator
=== RUN   TestConfig
=== RUN   TestConfig/Propagator
=== RUN   TestConfig/Propagator/DefaultValue
=== RUN   TestConfig/Propagator/EnvironmentVariableOverride
--- PASS: TestConfig (0.00s)
    --- PASS: TestConfig/Propagator (0.00s)
        --- PASS: TestConfig/Propagator/DefaultValue (0.00s)
        --- PASS: TestConfig/Propagator/EnvironmentVariableOverride (0.00s)
PASS
ok      github.com/signalfx/splunk-otel-go/distro       0.154s

[pellared]

This PR is blocked by #1172

[codecov-commenter]

Codecov Report

Merging #1171 (08a7fc4) into main (89df9c8) will decrease coverage by 0.76%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main    #1171      +/-   ##
==========================================
- Coverage   79.21%   78.44%   -0.77%     
==========================================
  Files          55       55              
  Lines        2771     2719      -52     
==========================================
- Hits         2195     2133      -62     
- Misses        528      536       +8     
- Partials       48       50       +2     

Flag	Coverage Δ
Linux	78.44% <100.00%> (-0.41%)	⬇️
Windows	?
macOS	74.62% <100.00%> (-0.48%)	⬇️

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

Impacted Files	Coverage Δ
distro/config.go	100.00% <100.00%> (ø)
distro/otel.go	65.57% <100.00%> (-0.56%)	⬇️
...n/github.com/lib/pq/splunkpq/internal/connector.go	51.75% <0.00%> (-5.03%)	⬇️

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