Build model relation methods without ConnectionInterface param

[mringler]

First draft for removing the ConnectionInterface parameter from relation methods by setting configuration parameter generator.omitConnectionInterfaceParameterOnRelationMethods to true.

Example:

    /**
     * @param \Propel\Runtime\ActiveQuery\Criteria|null $criteria
     * @param \Propel\Runtime\Connection\ConnectionInterface|null $con
     *
     * @return \Propel\Tests\Bookstore\Base\Collection\BookCollection
     */
    public function getBooks(?Criteria $criteria = null, ?ConnectionInterface $con = null): BookCollection
    {

becomes

    /**
     * @param \Propel\Runtime\ActiveQuery\Criteria|null $criteria
     *
     * @return \Propel\Tests\Bookstore\Base\Collection\BookCollection
     */
    public function getBooks(?Criteria $criteria = null): BookCollection
    {

Not sure if this matches #41 as there is still the ?Criteria $criteria = null param.

Manual setup passes sniffer and linter, but no tests yet.

[oojacoboo]

@mringler nice! And yea, until the getter is clean, the model is still polluted with Propel specific implementation details. Meaning, the Criteria needs to go as well, or at least be a setting to be optionally removed. If someone wants to further filter a relation, they could define the method in their child class and add their filter logic. Forcing that thing down on a child class means it's impossible to have pure/clean domain models.