[New Extension]: first_last_agg

### Is there an existing issue for this extension request?

- [x] I have searched for an existing issue, and could not find a duplicate request.

### Extension Name

first_last_agg

### Project Repository URL

https://github.com/wulczer/first_last_agg

### Extension Website URL (Optional)

https://github.com/wulczer/first_last_agg

### Short Description

A simple extension providing two aggregate functions, last and first aggregate functions, operating on any element type and returning the last or the first value of the group.

### Main LICENSE Link

https://pgxn.org/dist/first_last_agg/

### License Compliance

- [x] The extension's license (linked above) complies with the list of allowed licenses.

### Known Dependent Extensions

None

### Component Owner and Maintenance Commitment

- [x] I/My organization commit to becoming the Component Owner and maintaining the extension image in the future.

### Additional Notes (Optional)

https://pgxn.org/dist/first_last_agg/ says the license is PostgreSQL. The source code only says `Copyright (c) 2011, PostgreSQL Global Development Group` though.

### GitHub Handles of Component Owners

ibotty

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

La issue nomina l’estensione PostgreSQL first_last_agg e il relativo repository upstream, ma non indica file, test o punti di ingresso dell’implementazione. Esamina le integrazioni delle immagini delle estensioni esistenti in questo repository, quindi verifica i dettagli relativi alla licenza e alla manutenzione dell’upstream tramite i link PGXN e al codice sorgente forniti. Il lavoro è completato quando l’estensione è integrata secondo le convenzioni del repository e le relative informazioni sulla licenza sono state confermate.

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