fix: pass if table is already removed on upgrade

[sadpandajoe]

SUMMARY

Looks like if you try to run the migrations but the sl_ tables don't already exist the migrations will fail. This will just pass the upgrade check if the table doesn't already exist.

• Added a has_table function to return a boolean if the table exist or not
• Updated drop_fks_for_table to handle sqlite in the function

BEFORE/AFTER SCREENSHOTS OR ANIMATED GIF

TESTING INSTRUCTIONS

ADDITIONAL INFORMATION

• [ ] Has associated issue:
• [ ] Required feature flags:
• [ ] Changes UI
• [ ] Includes DB Migration (follow approval process in SIP-59)
  • [ ] Migration is atomic, supports rollback & is backwards-compatible
  • [X] Confirm DB migration upgrade and downgrade tested
  • [ ] Runtime estimates and downtime expectations provided
• [ ] Introduces new feature or API
• [ ] Removes existing feature or API