Add db commands to the CLI for database management

[OceanOak]

This PR:

• Add db CLI command for creating and managing user databases
• Re-introduce accounts table and add account_id to canvases, so each account gets its own canvas and DBs

Test example:

DARK_ACCOUNT=Darklang ./scripts/run-cli type Darklang.Test.User '{ name: String; email: String; age: Int64 }'
✓ Created type: Darklang.Test.User

DARK_ACCOUNT=Darklang ./scripts/run-cli db Users Darklang.Test.User
Created database: Users (type: Darklang.Test.User)

DARK_ACCOUNT=Darklang ./scripts/run-cli db set Users alice '{ name = "Alice"; email = "alice@example.com"; age = 30L }'
Set alice in Users

DARK_ACCOUNT=Darklang ./scripts/run-cli db set Users john '{ name = "John"; email = "john@examp
le.com"; age = 25L }'
Set john in Users

DARK_ACCOUNT=Darklang ./scripts/run-cli db view Users

Key            name           email          age            
──────────────────────────────────────────────
alice          "Alice"        "alice@example.com"30             
john           "John"         "john@examp"   25             

2 row(s)

[StachuDotNet]

Great work on this.