fix: mongo explain queries should always return as an array of results

[cbaker6]

New Pull Request Checklist

• [x] I am not disclosing a vulnerability.
• [x] I am creating this PR in reference to #7442.

Issue Description

explain for mongo is currently returning an object when returning results. This conflicts with trying to decode explain results because it should return an array of objects when using find instead of a single object.

This error was probably not seen before because JS and some other languages are "not strongly typed," meaning the language doesn't care if a single object is returned instead of an array of objects. This is not the case with the Swift SDK.

This also requires a fix to the JS SDK for proper support along with any other SDK that adapted to the bug.

This will be a breaking change as devs who use mongo probably programmed to the bug mentioned above. Close #7442

Originally discussed on community.parseplatform.org

Related issue: #7442

Approach

Make find in the MongoStorageAdapter return an array of objects to conform to the way it's suppose to return results.

TODOs before merging

• [x] Fix current test cases that were adapted to bug
• [x] Add entry to changelog

[codecov[bot]]

Codecov Report

Merging #7440 (7a40fa0) into alpha (45d29cc) will decrease coverage by 0.02%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##            alpha    #7440      +/-   ##
==========================================
- Coverage   93.93%   93.90%   -0.03%     
==========================================
  Files         181      181              
  Lines       13267    13267              
==========================================
- Hits        12462    12459       -3     
- Misses        805      808       +3     

Impacted Files	Coverage Δ
src/Adapters/Storage/Mongo/MongoStorageAdapter.js	92.37% <100.00%> (ø)
src/Adapters/Files/GridFSBucketAdapter.js	79.50% <0.00%> (-0.82%)	:arrow_down:
src/RestWrite.js	93.76% <0.00%> (-0.32%)	:arrow_down:

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[cbaker6]

I'll submit the JS fix later today as that will be needed for the test cases. Essentially, an explainable first is needed.

[mtrezza]

⚠️ Important change for merging PRs from Parse Server 5.0 onwards!

We are planning to release the first beta version of Parse Server 5.0 in October 2021.

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[mtrezza]

Concerted to draft:

• If this means a breaking change, we may as well break for a more sustainable solution, see https://github.com/parse-community/parse-server/pull/7440#discussion_r678916891.
• We don't introduce breaking changes this way anymore, we'd phase them in if possible.

[parse-github-assistant[bot]]

Thanks for opening this pull request!

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