[explorer] Update all explorer URL references

[Jordan-Mysten]

We're moving to a network-agnostic explorer, and this updates all references to point to the new explorer. We'll also set up a redirect so any missed paths should be fine.

[github-actions[bot]]

💳 Wallet Extension has been built, you can download the packaged extension here: https://github.com/MystenLabs/sui/actions/runs/3448123396#artifacts

[randall-Mysten]

thanks for updating docs! I approve content changes, leaving formal approval for Eng