feat(pg): remove support for pg v7

[blumamir]

pg instrumentation claimed support for v7 and v8.

For version 7, it is not compatible to node>=14 here and we were not running any tests for this version since we dropped support for node 8,10,12.

Also, pg version 7 last published version is 3 years old and it has 120K npm weekly downloads vs around 2M for the latest v8 versions.

Since we don't actually run tests for it and do not expect pg@7 to work with our supported node versions, I think it is safe to remove it from the supported pg versions

[codecov]

Codecov Report

Merging #1393 (fd5c422) into main (3e76af6) will decrease coverage by 0.27%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1393      +/-   ##
==========================================
- Coverage   96.10%   95.84%   -0.27%     
==========================================
  Files          14       18       +4     
  Lines         898     1226     +328     
  Branches      192      264      +72     
==========================================
+ Hits          863     1175     +312     
- Misses         35       51      +16     

Impacted Files	Coverage Δ
...elemetry-instrumentation-pg/src/instrumentation.ts	91.21% <ø> (ø)
...tapackages/auto-instrumentations-node/src/utils.ts	98.21% <0.00%> (ø)
...node/opentelemetry-instrumentation-pg/src/utils.ts	98.31% <0.00%> (ø)
...try-instrumentation-pg/src/enums/AttributeNames.ts	100.00% <0.00%> (ø)