Coerce configuration input

[medikoo]

So far version validation was strict, we've just allowed null values (properties with null were removed for validation), still that imposes not justified burden (as e.g. case described here: #8285 (comment))

This patch ensures that null valued properties are cleared from resolved config not only for validation but also for it's further processing, and more importantly it coerces primitive values so they adhere to schema.

Coercion is done per rules described here: https://ajv.js.org/coercion.html (with array coercion turned off at this point, as it seems it be problematic: ajv-validator/ajv#1294)

[codecov-commenter]

Codecov Report

Merging #8319 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #8319      +/-   ##
==========================================
- Coverage   88.02%   88.02%   -0.01%     
==========================================
  Files         249      249              
  Lines        9312     9308       -4     
==========================================
- Hits         8197     8193       -4     
  Misses       1115     1115              

Impacted Files	Coverage Δ
lib/configSchema.js	100.00% <ø> (ø)
...lugins/aws/package/compile/events/httpApi/index.js	92.59% <ø> (ø)
lib/plugins/aws/provider/awsProvider.js	93.04% <ø> (ø)
lib/classes/ConfigSchemaHandler/index.js	89.10% <100.00%> (-0.42%)	⬇️
...ib/plugins/aws/package/compile/events/alb/index.js	100.00% <100.00%> (ø)
...ins/aws/package/compile/events/cloudFront/index.js	99.32% <0.00%> (ø)

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