This diff adds to miniooni support for using the torsf tunnel. Such a
tunnel consists of a snowflake pluggable transport in front of a custom
instance of tor and requires tor to be installed.
The usage is like:
```
./miniooni --tunnel=torsf [...]
```
The default snowflake rendezvous method is "domain_fronting". You can
select the AMP cache instead using "amp":
```
./miniooni --snowflake-rendezvous=amp --tunnel=torsf [...]
```
Part of https://github.com/ooni/probe/issues/1955
Part of https://github.com/ooni/probe/issues/2184, because I wanted
to allow swapping commands and options more freely.
As a side effect, this PR closes https://github.com/ooni/probe/issues/2248.
AFAICT, every usage that was legal before is still legal. What has
changed seems the freedom to swap commands and options and a much
better help that lists the available options.
This diff splits miniooni's implementation in smaller and more
easily tractable blocks ahead of future refactoring.
I'm trying to make `miniooni oonirun -i URL` as possible as
`miniooni -i URL oonirun`, because users typically expect this
kind of flexibity from modern Unix commands.
Part of https://github.com/ooni/probe/issues/2184
