Ensured Cloud Event completness by adding assertion for required attributes as well as generation of default values for attributes such as ID and SPECVERSION

Added initial test to validate builder and utils

This reverts commit 1925b490.

There was a TODO in the cloud events section of the function catalog.
This extracts that into a strategy and autoconfigures it:
CloudEventOutputMessageHeaderEnricher.

Without this change a function with a Tomcat wrapper cannot be compiled
to a native image (or it can but it fails at runtime) because there
are lambda$$$ methods in the byte code that refer to missing types.

Resolves #611

Given that s-c-f-web always sends input as Flux, it creates issues for Function<Mono, Mono>, so this fixes it
Resolves #609

Resolves #608

Helps with native images

Resolves #422
Resolves #606

Related to GH-422 and GH-606

This commit effectively a merge of work with #607 and simplifies the following
- CloudEventAttributesProvider now provides CloudEventAttributes initialized with defaults to be set by the user
- In HTTP RequestProcessor the logic of sanitizing headers was improved to ensure that correct prefix is applied

Resolves #607

Related to #422,606

Normalizing in this context means converting it to binary-mode so the rest of the processing logic is the same.
Added support for canonical attribute names. Now, internally any attribute can be set as 'ce_' regardless where it came from are where it goes to as the frameork will be able to recognize both
Removed CloudEventMessageConverter
Renamed CloudEventAttributes to CloudEventAttributesHelperas it is better suited to what it actually does

Related to #422 and #606