Fix hidden side effect in TableUpdateMetadata

[stettix]

TableUpdateMetadata has an apply method that generates a random commit ID. This is bad for two reasons:

• It's easy to forget to pass a commit ID when creating a TableUpdateMetadata and then you'll get a random one instead.
• It's not referentially transparent.

We should remove this apply method and add an effectful constructor in CommitId instead, and use this where appropriate. E.g. something like this:

  object CommitId {
     def create[F[_]](implicit F: Sync[F]): F[CommitId] =
      F.delay(UUID.randomUUID()).map(uuid => CommitId(uuid.toString))
  }

Tracking here as a separate issue as it touches quite a bit of code in core (not in any particularly complex way though).