Make allowedMetaFields option consistent across plugins

[aduh95]

Initial checklist

• I understand this is a feature request and questions should be posted in the Community Forum
• I searched issues and couldn’t find anything (or linked relevant results below)

Problem

allowedMetaFields sometimes defaults to null, sometimes to []. null is a confusing value.

Solution

• Make it support boolean values, true meaning all files are allowed, false none are allowed (same as []).
• Make it default to false on all plugins, so it's always opt-in to send metadata.

Alternatives

• Make it default to trus on all plugins, so it's always opt-out to not send metadata.