WIP! Make sure custom relations work out with new alias strictness.

[dereuromark]

Refs #1012

So basically 5.1 and the more strict relation-handling ("Association alias Countries is already set") kinda broke the non documented feature of custom relationship baking.
Even though it was just baked wrongly with always the same Countries relation.

This PR already adds the expected aliasing back ensuring there is no collision, and having the correct name in the process for most cases:

[
  'belongsTo' => [
    (int) 0 => [
      'alias' => 'Countries',
      'foreignKey' => 'country_id',
      'className' => 'Countries'
    ],
    (int) 1 => [
      'alias' => 'BillingCountries',
      'foreignKey' => 'billing_country_id',
      'className' => 'Countries'
    ],
    (int) 2 => [
      'alias' => 'ShippingCountries',
      'foreignKey' => 'shipping_country_id',
      'className' => 'Countries'
    ]
  ],
  'hasOne' => [],
  'hasMany' => [],
  'belongsToMany' => []
]

as example for

Countries

• id

Users

• id
• country_id
• billing_country_id
• shipping_country_id

This would still need to get finished up inside Bake Model command of course.
Maybe someone wants to help out here.

[markstory]

Suggested change

	protected function alias(array $association): string
	protected function createAssociationAlias(array $association): string

alias is a pretty general term, I think a more specific name could be helpful for future us.

[markstory]

Suggested change

	$alias = $this->alias($association);
	$alias = $this->createAssociationAlias($association);