10s block time

Context

This is similar to !7017 (merged), except that it reduces block times to 10s instead of 15s.

Constant also related to block time that may need to be updated:

• max_timestamp_drift, last changed in !2532 (merged)
• synchronization.latency, last changed in !9138 (merged)

Doc update are in !11367 (merged)

Manually testing the MR

Run the newly added test with:

dune exec tezt/tests/main.exe -- --file baker_test.ml rewards --verbose

CI green for other tests

Checklist

• n/a Document the interface of any function added or modified (see the coding guidelines)
• n/a 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