feat(eap): Add AttributeValue data structure

[Dav1dde]

Needed for #4592 and future EAP envelope items (Spans).

The PR itself only adds the data structure, but it is still unused, to prevent clashes with the still different OurLogs implementation, that one was renamed (until it is removed).

TODO:

• Implement ProcessValue
• Figure out PII

#skip-changelog

[Dav1dde]

This approach of 'validating' during deserialization is not feasible due to needing large boilerplate of manually implementing macros and still leaving open misconfigurations through the Other hatch. Instead just keeping it as a struct with a separate validation in the processor is the better appraoch.