Allow fine-grained meta index configuration

[lava]

📝 Checklist

• All user-facing changes have changelog entries.
• The changes are reflected on docs.tenzir.com/vast, if necessary.
• The PR description contains instructions for the reviewer, if necessary.

🎯 Review Instructions

Review this pull request commit-by-commit.

[dominiklohmann]

This whole PR needs a changelog entry and a docs update. We should also clarify in there how/whether this affects the #skip and #index=hash attributes.

I had some general questions inline, most importantly on the configuration section.

[tobim]

This looks alright to me, but I would like to see a unit test that verifies that synopses are constructed with the correct parameters.

[tobim]

Thanks for adding the test!