[nv16] niceties for development bundle loading

[vyzo]

This adds some niceties for development bundle loading; see the README.

Related Issues

See #8625

[vyzo]

unexpected test failures are from github hiccups:

2022-05-16T12:13:33.093Z	ERROR	bundle-fetcher	bundle/bundle.go:59	error fetching bundle builtin-actors-mainnet: all attempts to fetch https://github.com/filecoin-project/builtin-actors/releases/download/b71c2ec785aec23d/builtin-actors-mainnet.sha256 failed
panic: error fetching bundle for builtin-actors version 8: error fetching bundle: all attempts to fetch https://github.com/filecoin-project/builtin-actors/releases/download/b71c2ec785aec23d/builtin-actors-mainnet.sha256 failed

goroutine 1 [running]:
github.com/filecoin-project/lotus/cli.init.0()
	/home/circleci/project/cli/init.go:19 +0x5a

Exited with code exit status 2

[vyzo]

we might want to cache /tmp/lotus-testing in CI.

[raulk]

@vyzo something seems to be broken in GitHub for builtin-actors because even release edit pages return a 404.

[raulk]

@vyzo It's a weird to rely on a string convention when we have a TOML schema to which we can add properties. I would suggest that if you want to treat a bundle as a development release, you should specify the dev = true key for that bundle in its TOML table.

Also, we should add a path attribute to load the bundle from the local filesystem when it's specified.

[vyzo]

sure, can do.

[raulk]

LGTM, except for the comments. Approving in anticipation, but @arajasek should comment too.

[arajasek]

This LGTM!