After #16203 was fixed (in PR #16353), we can now create an Alternator table that uses tablets instead of vnodes by setting the experimental:initial_tablets tag on the new table.

The goal of this issue is to make this behavior the default. I.e., every new Alternator table should use tablets, not vnodes.

Before we can enable tablets on Alternator by default, we need to make sure that 100% of the Alternator features supported with vnodes will also work correctly with tables. PR #16353 fixed one major broken feature (secondary indexes), but additionally the following features are thought to be broken and will need to be fixed:

1. Alternator Streams needs CDC, which isn't yet supported on tablets (Support CDC with tablets #16317).
2. Alternator TTL doesn't work (Support tablets in Alternator TTL #16567)

To be sure this issue is really done, we'll need to run all Alternator tests - both in-tree test/alternator and dtest's Alternator tests - using tablets and see all of them pass. Right now, all Alternator Streams and Alternator TTL tests fail when tablets are forced in Alternator.