Linked the PDO/DBAL Session article from the Doctrine category
minor #4649 Linked the PDO/DBAL Session article from the Doctrine category (javiereguiluz)

This PR was squashed before being merged into the 2.3 branch (closes #4649).

Discussion
----------

Linked the PDO/DBAL Session article from the Doctrine category

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | all
| Fixed tickets | #4416

Commits
-------

cb4784a Linked the PDO/DBAL Session article from the Doctrine category