Overuse of "metadata" as a phrase

Metadata is defined as data that describes other data. There are a lot of places in the code where "metadata" is used incorrectly --that is, it isn't "metadata" is should just be "data", "extraData", "auxillaryData", or similar. The most prominent example of this is the `pkg.Package.Metadata` field.

We should be more careful with this word choice and replace any instance that isn't accurate with another word.

Note: this has been exposed in the syft JSON format as well, so any change here may have impacts with the JSON schema.

Start by reviewing the `pkg.Package.Metadata` field and its use in the code, then check how it appears in the Syft JSON format and schema. Identify uses of “metadata” that do not describe data about other data; done means those uses have accurate names and any JSON schema impacts are addressed.

Written by the indexing model from the issue text.