Validate lengths of arguments used in Validator module methods and endpoints

[bobanm]

What was the problem?

This PR resolves #8914

How was it solved?

• All relevant Validator methods now validate argument lengths using the new private method _validateLengths()
• Updated validateBLSKey endpoint request schema to validate lengths of BLS key and proof of possession.
• BONUS: improved tests to use constants for lengths instead of specifying number literals 😎

How was it tested?

• Implemented additional tests for _validateLengths() method
• All tests OK 👌🏻

[shuse2]

change LGTM, the test/lint is failing

[codecov]

Codecov Report

Merging #8920 (ae0cf98) into release/6.0.0 (108b1ce) will decrease coverage by 0.01%.
The diff coverage is 93.75%.

❗ Current head ae0cf98 differs from pull request most recent head b5809df. Consider uploading reports for the commit b5809df to get more accurate results

@@                Coverage Diff                @@
##           release/6.0.0    #8920      +/-   ##
=================================================
- Coverage          83.61%   83.61%   -0.01%     
=================================================
  Files                601      601              
  Lines              22520    22520              
  Branches            3323     3319       -4     
=================================================
- Hits               18830    18829       -1     
- Misses              3690     3691       +1     

Files Changed	Coverage
framework/src/modules/validators/method.ts	93.33%
framework/src/modules/validators/schemas.ts	100.00%