port filter helper to holochain-0.2 branch

[pdaoust]

Companion to #128. I haven't smoke-tested it, but it does pass local CI.

[ThetaSinner]

@pdaoust Thank you for creating this. I would like to get the changes onto main first then we'll port the commits from there. That should make it easier to keep track of for maintenance than having two separate changes targeting different branches

[ThetaSinner]

I'm going to close this because the back-porting to 0.1/0.2 should now happen after the referenced PR is merged