Relax timeout for sending activities

[Nothing4You]

Lemmy considers timeouts during activity sending as retryable errors. While it is frequently enough to retry sending the same activity again after the original submission attempt resulted in a timeout, allowing the receiving side to use more time for synchronous processing should reduce the number of retries needed overall and improve overall compatibility.

Some ActivityPub software, such as Mastodon, implements a queue for processing received activities asynchronously, which allows immediately returning a response for activity submissions. Other software, such as Lemmy or Hubzilla implement synchronous processing of activities before returning a response.

ActivityPub does not specify specific timeouts to be used: https://github.com/w3c/activitypub/issues/365