stacks-explorer link should be devnet explorer

[tippenein]

When running clarinet devnet start the link for the stacks-explorer should go to devnet, not mainnet.

The correct url is http://localhost:8000/?chain=testnet&api=http://localhost:3999

The work to fix this has been mostly done here but currently that branch will stall on "preparing container".

This issue is to get that status update to reflect a correct link