Accept multiple URLs for checkpoint sync

[MegaRedHand]

We currently accept a URL with --checkpoint-sync-url, to fetch the latest finalized state from a server. We could accept multiple such URLs for redundancy. For backwards compatibility, we should still accept the current --checkpoint-sync-url <url> form, however, we want to also accept --checkpoint-sync-url <url-1>,<url-2> or --checkpoint-sync-url <url-1> --checkpoint-sync-url <url-2> forms.

[ava-world]

i will be working on this issue

[Aliemeka]

I need more context on this @MegaRedHand. Do you still want people to send single urls and multiple urls alternatively. Or should it be changed to support multiple only.

I want to work on this, I just need clarification

[MegaRedHand]

I added a bit more info. We want to accept both single URL or multiple URL formats. We want this to be backwards compatible. For now, we should just try with the first URL, then try with the second one, and so on until we either finish checkpoint-sync or run out of URLs.