styleguide: tests goroutine leaks and naming

[pellared]

1. Add rules to style guide to have more consistent test names and to increase their stability.

2. Rename tests that verifies concurrency safety to have ConcurrentSafe as suffix (I think I found most of them).

3. internal/global: fix goroutine leaks in tests. Fixes Data race in internal/global/internal_logging.go #4264

   Testing:

   $ go test -race -count=1000
   PASS
   ok      go.opentelemetry.io/otel/internal/global        233.443s
   

   Next week, I plan to check if tests in other packages have the same problem

If requested I can split this to separate PR's. However, I think it may be easier to review everything at once as the code changes give context to the new rules introduced in the style guide.

[codecov]

Codecov Report

Merging #4348 (1a2a0dd) into main (cbc5890) will decrease coverage by 0.1%.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #4348     +/-   ##
=======================================
- Coverage   83.4%   83.4%   -0.1%     
=======================================
  Files        184     184             
  Lines      14360   14360             
=======================================
- Hits       11988   11986      -2     
- Misses      2145    2147      +2     
  Partials     227     227             

see 1 file with indirect coverage changes