Add pg_qualstats as managed extension

[pha91]

Hi @ALL

we're planning to use CNPG for our new microservice application. Our developer are big fans of the pg_qualstats extension, which helps a lot while optimizing the database and queries.
Would it be possible to add this extension to the default image?

Could implement it by my own but maybe it will help also some guys in the community

Best regards
Philipp