Add prysmctl subcommand to download unfinalized blocks

[lyzs90]

What type of PR is this?

Feature

What does this PR do? Why is it needed?

• Add a subcommand to dump unfinalized blocks to zip file

bazel run //cmd/prysmctl ub dl —- —-beacon-node-host=<beacon-node-url> --outdir=<abs-path-to-dir>

• Add a retry flag on the beacon client as the infura free node was quite unusable without this during testing

Which issues(s) does this PR fix?

Fixes #11180

Other notes for review

[rauljordan]

Hi @lyzs90 thanks for this contribution - would be awesome to still get this checked in! There are a few build errors that are present in your PR, but looking good for the most part. Let us know if you need any help

[james-prysm]

@lyzs90 any interest in fixing this PR? I've switched it into draft mode in the mean time