Upgrade package to Plone 6

[erral]

• I signed and returned the Plone Contributor Agreement, and received and accepted an invitation to join a team in the Plone GitHub organization.
• I verified there aren't any other open pull requests for the same change.
• I followed the guidelines in Contributing to Plone.
• I successfully ran code quality checks on my changes locally.
• I successfully ran tests on my changes locally.
• If needed, I added new tests for my changes.
• If needed, I added documentation for my changes.
• I included a change log entry in my commits.

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Changes made:

• Apply plone/meta
• Update dependencies
• Support only Plone 6

We will have a release for Plone 6 with these changes, and then do another release with implicit namespaces