Always set $info['namespace'] on database connection info

Problem/Motivation

We have a method to determine the db driver namespace if it is not provided - \Drupal\Core\Database\Database::getDatabaseDriverNamespace() - which supports supports fallling back to the core db driver namespace. This results in the connection info sometimes having the driver namespace and sometimes not.

Proposed resolution

Always set $info['namespace'] instead of using a method.

Remaining tasks

User interface changes

None

API changes

\Drupal\Core\Database\Database::getDatabaseDriverNamespace() is deprecated in Drupal 9.1.x

Data model changes

None

Release notes snippet

N/a