Add builder for `SchemaValidatorsConfig`

[justin-tay]

This creates a SchemaValidatorsConfig.Builder to create SchemaValidatorsConfig instances. This also updates the documentation and release notes assuming that the next release will be 1.4.1. This also updates all the tests that used the constructor to the builder.

This is was done in order to

• Eventually make SchemaValidatorsConfig immutable. For now this just deprecates the SchemaValidatorsConfig constructor as this part of the public API is quite widely used. Instances by the builder will throw UnsupportedOperationException when setters are called.
• Make changes to the defaults in SchemaValidatorsConfig. For instance setting PathType.JSON_POINTER as default as this aligns better with the spec. The changes in defaults only apply if the builder was used to construct the instance so existing codes using the constructor are unaffected and can migrate when it suits them.

Note that there are differences in defaults from the builder vs the constructor.

The following builder creates the same values as the constructor previously.

SchemaValidatorsConfig config = SchemaValidatorsConfig.builder()
    .pathType(PathType.LEGACY)
    .errorMessageKeyword("message")
    .nullableKeywordEnabled(true)
    .build();

The following configurations were renamed with the old ones deprecated

• handleNullableField -> nullableKeywordEnabled
• openAPI3StyleDiscriminators -> discriminatorKeywordEnabled
• customMessageSupported -> errorMessageKeyword

The following defaults were changed in the builder vs the constructor

• pathType from PathType.LEGACY to PathType.JSON_POINTER
• handleNullableField from true to false
• customMessageSupported from true to false

When using the builder custom error messages are not enabled by default and must be enabled by specifying the error message keyword to use ie. "message".

Deprecated Code	Replacement
SchemaValidatorsConfig config = new SchemaValidatorsConfig();	SchemaValidatorsConfig config = SchemaValidatorsConfig().builder().pathType(PathType.LEGACY).errorMessageKeyword("message").nullableKeywordEnabled(true).build();
config.setEcma262Validator(true);	builder.regularExpressionFactory(JoniRegularExpressionFactory.getInstance());
config.setHandleNullableField(true);	builder.nullableKeywordEnabled(true);
config.setOpenAPI3StyleDiscriminators(true);	builder.discriminatorKeywordEnabled(true);
config.setCustomMessageSupported(true);	builder.errorMessageKeyword("message");

[stevehu]

@justin-tay Please let me know if we should release the 1.4.1 tag. Thanks.

[justin-tay]

@stevehu Think we should release the 1.4.1 tag. Thanks!