Disabled snapshots with the always indexing strategy

This MR is an alternate solution for issue !4715 (merged): we disable the snapshot export for nodes using the non-default indexing strategy. This is a breaking change.

Mind updating !7522 (merged) (doc MR) when merged.

Closes

#4715 (closed)

Context

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR