Simplify ColumnType usage

[ra0x3]

• This came up during discussions with @AlicanC
• We have several ColumnTypes that all effectively map to the same type on the backend
• We should scope down the number of public ColumnTypes we're using
• We should also align our scalar names to be more inline with the Fuel ecosystem (e.g., change UInt8 to U8)
• This will be merged into https://github.com/FuelLabs/fuel-indexer/tree/feature/dynamic-graphql

[ra0x3]

Though this was merged into a feature branch, will leave this open until the feature branch is merged into develop and the docs are updated accordingly