chore: remove legacy code

[jonaro00]

Description of change

The 💣 is here.
Removes all shuttle.rs code, keeping only what is used on shuttle.dev. 🫡
Review at your own risk (not recommended).
(Shoutout to twitter/the-algorithm#122)

• Lines of code (onefetch -e examples): 40315 -> 9979
• Axum hello-world dependency tree: 279 -> 217
• cargo-shuttle release build dependency tree: 485 -> 432

Breaking changes:

• Removed legacy CLI commands and options
  • cargo shuttle now targets shuttle.dev
• Removed nearly all legacy crate APIs
• Removed unsupported crates & resources
• Removed some crate features
• Changed module location of some shuttle-common items, added "tables" feature
• Bumped postgres version in local provisioner to 16, to match current RDS and shared databases
• Fixed shuttle run to use same secrets loading logic as shuttle deploy, which is more strict, instead of using legacy logic

How has this been tested? (if applicable)

• Updated CLI tests to use new platform. Added back rocket_postgres CLI local run test using DB.
• Other than that tests were just removed ;)

[jonaro00]

@chesedo @oddgrd @brokad @iulianbarbu @christos-h @Kazy and other contributors,
It has been a pleasure 🫡

[oddgrd]

Thanks! 💥