Feature/riseupvpn config

[hellais]

Create new ooniprobe service to support OpenVPN experiment.

Add experimental entrypoint to provision credentials to OpenVPN experiment.

• Single provider (riseup) for the MVP.
• Configurable "freshness" parameter to limit the query.
• Stub for inserting new credentials periodically.

This superseeds: #830

[codecov]

Codecov Report

Attention: Patch coverage is 99.48320% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 99.88%. Comparing base (e486936) to head (c01c576).
Report is 3 commits behind head on master.

❗ Current head c01c576 differs from pull request most recent head e99162c. Consider uploading reports for the commit e99162c to get more accurate results

Files	Patch %	Lines
...api/services/ooniprobe/src/ooniprobe/routers/v2.py	96.61%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##            master     #832      +/-   ##
===========================================
- Coverage   100.00%   99.88%   -0.12%     
===========================================
  Files           21       27       +6     
  Lines         1439     1771     +332     
  Branches       116      143      +27     
===========================================
+ Hits          1439     1769     +330     
- Misses           0        2       +2     

Flag	Coverage Δ
ooniauth	100.00% <ø> (ø)
ooniprobe	99.47% <99.47%> (?)
oonirun	100.00% <100.00%> (ø)

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[ainghazal]

looks good to me, this is minimal and great to test the experiment; left some comments for future improvements since we have some of the discussion fresh.

the only change I see would be to reduce the frequency to a day (or less) so that we can test the updates.

to minimize migrations, perhaps it'd be good to deploy & test this branch and then pile up changes like metadata and perhaps a nicer abstraction for organizing measurement turnover. I'd suggest to have a conversation about that after landing the probe-cli experiment.