Update OZ contracts to version 5.2.0 and remove solidity-stringutils dependency

[ernestognw]

Description

Required for OpenZeppelin/openzeppelin-community-contracts#182

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• I have discussed with the team prior to submitting this PR
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• New and existing unit tests pass locally with my changes

[ernestognw]

Need to validate tests are working properly before it's ready

[ernestognw]

Gas diff:

-JwtRegistryTest_stringToArray:test_stringToArray() (gas: 28540)
+JwtRegistryTest_stringToArray:test_stringToArray() (gas: 10981)