Move some netty converters to SPI

[yawkat]

Move some converters from NettyConverters into a new converter registrar that does not require further dependencies from the application context. This allows the registrar to be loaded into the default conversion service with no app context present.

This is a workaround for #7948, and fixes micronaut-projects/micronaut-aws#1452 .

[dstepanov]

Some of the converters that are using conversionService are using convertors from the same class. Maybe we can make them static fields and use them directly or use ConversionServiceDEFAULT? The first option removes an option to override them, but that might be fine.

[yawkat]

sounds sensible, ive moved the http data converters to the spi class.

[sonarqubecloud]

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