[Request]: Add build matrix into CI pipeline to check minimally supported Flutter version compatibility

### Plugin

All plugins

### Use case

Recently there was an issue https://github.com/fluttercommunity/plus_plugins/issues/1960 which made it obvious that current testing of changes done with pipelines setup isn't enough. Thus, it would be good to test changes not only against latest stable Flutter version, but also against the minimally supported one to be sure no issues introduced for projects with not so fresh Flutter version.

### Proposal

Add build matrix: https://docs.github.com/en/actions/using-jobs/using-a-matrix-for-your-jobs to check all PRs against minimally supported Flutter versions as well.

Inizia esaminando la configurazione della pipeline CI del repository e le versioni minime supportate di Flutter per i plugin. Usa la documentazione sulle matrici di GitHub Actions collegata nella proposta, quindi verifica che le pull request vengano eseguite sia con l’ultima versione stabile di Flutter sia con la versione minima supportata di Flutter per tutti i plugin.

Scritto dal modello di indicizzazione a partire dal testo della issue.