docs: add Blobstream update rate/schedule

[nuke-web3]

https://docs.celestia.org/how-to-guides/blobstream shows contracts, but not the rate/schedule.
I believe we have 1 hour updates for SP1 based verifiers universally now, but some will move to 5 minutes soon.

Perhaps mentioning a way to request a network be added via some form or other contact method that is monitored by the people who can make it happen.

cc @Ferret-san

[jcstein]

new column should be added for "Updated every" or similar, here https://docs.celestia.org/how-to-guides/blobstream#deployed-contracts