[CI][Dev] Document how to maintain `CROSSBOW_GITHUB_TOKEN`

### Describe the enhancement requested

We're using `CROSSBOW_GITHUB_TOKEN` for comment bot:

https://github.com/apache/arrow/blob/54ea6d5babb6a1841dbe50e1cb84ae6321cd64cb/.github/workflows/comment_bot.yml#L51-L58

We need to generate a token that has suitable scope (`contents:write actions:write workflows:write`, see also [#dev > ✔ Update Crossbow tokens @ 💬](https://arrow-dev.zulipchat.com/#narrow/channel/180245-dev/topic/.E2.9C.94.20Update.20Crossbow.20tokens/near/555410591)) and ask INFRA to set it GitHub Actions secret.

We have token expiration notification mechanism: https://lists.apache.org/list?builds@arrow.apache.org:lte=3y:CROSSBOW_GITHUB_TOKEN

But I don't know how to configure it...

### Component(s)

Continuous Integration, Developer Tools

Inizia da .github/workflows/comment_bot.yml alle righe 51-58 per capire come viene utilizzato CROSSBOW_GITHUB_TOKEN. Esamina la discussione Zulip collegata e i messaggi di notifica della scadenza del token, quindi documenta la generazione del token, gli scopes richiesti e la procedura per chiedere a INFRA di configurare il secret di GitHub Actions.

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