feat: explore transforming psiphon into a service

[bassosimone]

If we transform psiphon and tor into services, we should be able to get rid of crashing and other singleton issues.

Checklist

• I have read the contribution guidelines
• reference issue for this pull request:
• if you changed anything related to how experiments work and you need to reflect these changes in the ooni/spec repository, please link to the related ooni/spec pull request:
• if you changed code inside an experiment, make sure you bump its version number

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