Custom foreign key naming

[Edvinas01]

I'd like to specify a custom name for a foreign key:

object Users : IdTable<Long>("user") {

    override val id = long("id")
        .primaryKey()
        .autoIncrement("user_id_seq")
        .entityId()

    val documentId = reference(
        onDelete = ReferenceOption.SET_NULL,
        foreign = Documents,
        name = "document_id" // <- can set column name, but foreign key cannot be named.
    ).nullable()
}

However looking at current implementation, it seems that fk_${table_name}_${table_column}_${foreign_column} pattern is used and cannot be changed (notice how refName is constructed):

Exposed/src/main/kotlin/org/jetbrains/exposed/sql/Constraints.kt

Lines 40 to 51 in 062083e

	fun from(fromCol: Column<*>): ForeignKeyConstraint {
	require(fromCol.referee != null && (fromCol.onDelete != null || fromCol.onUpdate != null)) { "$fromCol does not reference anything" }
	val targetColumn = fromCol.referee!!
	val t = TransactionManager.current()
	val refName = t.quoteIfNecessary(t.cutIfNecessary("fk_${fromCol.table.tableName}_${fromCol.name}_${targetColumn.name}")).inProperCase()
	return ForeignKeyConstraint(refName,
	t.identity(targetColumn.table), t.identity(targetColumn),
	t.identity(fromCol.table), t.identity(fromCol),
	fromCol.onUpdate ?: ReferenceOption.NO_ACTION,
	fromCol.onDelete ?: ReferenceOption.NO_ACTION)
	}
	}

I guess it kinda relates to #470 which I've opened some time ago.