* feat(tunnel): introduce persistent tunnel state dir
This diff introduces a persistent state directory for tunnels, so that
we can bootstrap them more quickly after the first time.
Part of https://github.com/ooni/probe/issues/985
* fix: make tunnel dir optional
We have many tests where it does not make sense to explicitly
provide a tunnel dir because we're not using tunnels.
This should simplify setting up a session.
* fix(tunnel): repair tests
* final changes
* more cleanups
* chore: update dependencies
* chore: update user agent for measurements
* chore: we're now at v3.6.0
* chore: update assets
* chore: update bundled CA
* fix: address some goreportcard.com warnings
* fix(debian/changelog): zap release that breaks out build scripts
We're forcing the content of changelog with `dch`, so it's fine to
not have any specific new release in there.
* fix: make sure tests are passing locally
Notably, I removed a chunk of code where we were checking for network
activity. Now we don't fetch the databases and it's not important. Before,
it was important because the databases are ~large.
* fix: temporarily comment out riseupvn integration tests
See https://github.com/ooni/probe/issues/1354 for work aimed at
reducing the rate of false positives (thanks @cyBerta!)
