Add option to allow rule for column name

Background

Current by default the property is "lowercased".
If we want to custom it, we must use:

postgresql: {
  columnName: 'custom_name',
},

This is huge headache if system have hundred of tables hence possibly thousand of column names to customize.

Suggestion

We should provide an option in the connector level to allow users to compute column name as keep, lowercase, UPPERCASE, snake_case, camelCase, PascalCase, or custom function columnNameFn(propertyName: string) => string

E.g:

const dataSourceConfig = {
  name: 'db',
  connector: 'postgresql',
  columnNameComputation: 'snake_case',
  ...
}

Start by locating the connector-level configuration handling and the PostgreSQL column-name mapping; the issue provides no file or test entry point. Review how per-property columnName settings are currently applied. Done means the connector-level option supports the requested naming modes and a custom columnNameFn across the relevant mappings.