Remove use of oteltest in otelgocql

[MrAlias]

Replace the use of the oteltest package with the sdk/trace/tracetest package for the otelecho instrumentation. Do this in its own test module to not impose a dependency on the default SDK to the instrumentation user.

This uses a pre-release version of the sdk/trace/tracetest to prepare for the next release of otel-go.

Resolves #974

Part of open-telemetry/opentelemetry-go#2121

[codecov]

Codecov Report

Merging #998 (e0168d4) into main (ec88a56) will increase coverage by 0.1%.
The diff coverage is 85.1%.

@@           Coverage Diff           @@
##            main    #998     +/-   ##
=======================================
+ Coverage   74.9%   75.1%   +0.1%     
=======================================
  Files         71      76      +5     
  Lines       4462    4766    +304     
=======================================
+ Hits        3346    3580    +234     
- Misses       979    1036     +57     
- Partials     137     150     +13     

Impacted Files	Coverage Δ
...ation/github.com/gocql/gocql/otelgocql/observer.go	75.1% <70.9%> (ø)
.../github.com/gocql/gocql/otelgocql/internal/cass.go	95.1% <95.1%> (ø)
...entation/github.com/gocql/gocql/otelgocql/gocql.go	100.0% <100.0%> (ø)
...ion/github.com/gocql/gocql/otelgocql/instrument.go	62.5% <100.0%> (ø)
...ntation/github.com/gocql/gocql/otelgocql/config.go	65.9% <0.0%> (ø)