Fix locked key missing password message

[prd-fox]

• Remove unused key validation classes
• Add token for when a password was not provided
• Allow empty passwords to be valid

Note this also eagerly loads filesystem key files, and discards any errors that occurred. The thought process is that these errors will get picked up during validation of the config object.

Fixes #541

[codecov-io]

Codecov Report

Merging #580 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #580      +/-   ##
============================================
- Coverage     99.43%   99.43%   -0.01%     
+ Complexity     1643     1636       -7     
============================================
  Files           256      254       -2     
  Lines          4991     4979      -12     
  Branches        247      245       -2     
============================================
- Hits           4963     4951      -12     
  Misses            5        5              
  Partials         23       23

Impacted Files	Coverage Δ	Complexity Δ
...c/main/java/com/quorum/tessera/config/KeyData.java	100% <ø> (ø)	30 <0> (ø)	⬇️
...quorum/tessera/config/adapters/KeyDataAdapter.java	97.33% <ø> (ø)	18 <0> (ø)	⬇️
.../quorum/tessera/config/keypairs/InlineKeypair.java	100% <100%> (ø)	9 <0> (+2)	⬆️
...um/tessera/config/constraints/Base64Validator.java	100% <100%> (ø)	6 <0> (+1)	⬆️
...a/com/quorum/tessera/config/JaxbConfigFactory.java	100% <100%> (ø)	12 <0> (ø)	⬇️
...rum/tessera/config/keypairs/FilesystemKeyPair.java	100% <100%> (ø)	15 <8> (+3)	⬆️

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