Add node 18 to tests and remove EoL node versions

[dyladan]

Based on discussions we've had in several SIG meetings.

https://endoflife.date/nodejs

• API will continue to support old runtimes as long as is practical
• Allows us to update our CI tooling to versions which no longer support these deprecated runtimes

[codecov]

Codecov Report

Merging #3048 (64c6384) into main (b891509) will increase coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #3048      +/-   ##
==========================================
+ Coverage   92.65%   92.66%   +0.01%     
==========================================
  Files         187      187              
  Lines        6178     6178              
  Branches     1304     1304              
==========================================
+ Hits         5724     5725       +1     
+ Misses        454      453       -1     

Impacted Files	Coverage Δ
...emetry-core/src/platform/node/RandomIdGenerator.ts	93.75% <0.00%> (+6.25%)	⬆️

[pichlermarc]

Will the package.json "engines" fields be updated in a separate PR? 🤔

[dyladan]

Will the package.json "engines" fields be updated in a separate PR? 🤔

@open-telemetry/javascript-maintainers what do you think? Should the engines match the testing matrix? NPM doesn't check the engines field AFAIK but yarn does

[pichlermarc]

Will the package.json "engines" fields be updated in a separate PR? thinking

@open-telemetry/javascript-maintainers what do you think? Should the engines match the testing matrix? NPM doesn't check the engines field AFAIK but yarn does

I think the engines field also serves as documentation to some degree. We should also update the "Supported Runtimes" and "Node Support" Sections in README.md to reflect the changes in the testing setup.

[dyladan]

@legendecas @Flarna since your approvals I've added a lot of changes (particularly "engines" field) PTAL and make sure you're still happy with your approval

[rauno56]

Imho engines should be updated like it now is. The check can be bypassed if the user feels confident about it, but since they will be stepping into a wild west, it should be a conscious decision.