feat: add node 16 support; remove node 15 support

[mtrezza]

New Pull Request Checklist

• I am not disclosing a vulnerability.
• I am creating this PR in reference to an issue.

Issue Description

Node 15 reached its EOL; Node 16 is the current version

Related issue: #n/a

Approach

• remove node 15 from ci
• add node 16 to ci
• use node 16 as default

This appears to not be merely a CI change, but to require some minor changes in parse server / dependencies. Hence this PR will likely be a feat commit.

TODOs before merging

• Add entry to changelog
• Add changes to documentation (guides, repository pages, in-code descriptions)

[parse-github-assistant]

Thanks for opening this pull request!

• 🎉 We are excited about your hands-on contribution!

[codecov]

Codecov Report

Merging #7558 (4850953) into alpha (a359c02) will decrease coverage by 9.79%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##            alpha    #7558      +/-   ##
==========================================
- Coverage   93.99%   84.19%   -9.80%     
==========================================
  Files         181      181              
  Lines       13382    13382              
==========================================
- Hits        12578    11267    -1311     
- Misses        804     2115    +1311     

Impacted Files	Coverage Δ
...dapters/Storage/Postgres/PostgresStorageAdapter.js	2.47% <0.00%> (-92.90%)	⬇️
src/Adapters/Cache/RedisCacheAdapter.js	12.28% <0.00%> (-75.44%)	⬇️
src/Adapters/Storage/Postgres/PostgresClient.js	5.00% <0.00%> (-65.00%)	⬇️
src/batch.js	75.86% <0.00%> (-15.52%)	⬇️
src/ParseServerRESTController.js	82.08% <0.00%> (-14.93%)	⬇️
src/Adapters/Storage/Mongo/MongoStorageAdapter.js	90.10% <0.00%> (-2.59%)	⬇️
src/Controllers/UserController.js	95.34% <0.00%> (-2.33%)	⬇️
src/Controllers/FilesController.js	92.00% <0.00%> (-2.00%)	⬇️
src/Controllers/DatabaseController.js	92.63% <0.00%> (-1.16%)	⬇️
src/Controllers/index.js	96.66% <0.00%> (-1.12%)	⬇️
... and 6 more

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[funkenstrahlen]

👍

[mtrezza]

Yes, this has become stale because of other CI changes that have been prioritized. If anyone wants to pick this up in the meantime, please feel free.

[marvinroger]

This PR can now be closed 😉

[mtrezza]

Closing in favor of #7707