[Drizzle-kit]: Add "squash" command to CLI

[isaacwasserman]

This commit adds a 'squash' command to the drizzle-kit cli. This command allows users to combine a range of consecutive migrations. Squashing is particularly useful for cleaning up feature branches developed over multiple iterations that include many small, redundant, or contradictory migrations.

Changes:

• Adds squash command to CLI schema
• Implements squash command
  • Takes two custom arguments start (i) and end (j) representing the inclusive range of migrations to be merged
  • Combines migrations
    • Concatenates SQL files
    • Updates journal entry i to use snapshot from migration j
    • Removes journal entries i+1-j
    • Removes unused sql and snapshots
• No pre-existing code is modified or deleted
• Integration tests are included to ensure:
  • Basic functionality of CLI
  • Compatibility with existing generate and migrate commands

Note:
The squash command has a single known (and intentional) failure case when some environment has been migrated to version i < k < j.

Related issues/discussions: #2859 #4897 #3492