Added a job to renew user subscriptions

[levb]

Summary

• Added a simple job to renew all user subscriptions every 24 hours
• Increased the default subscription expiry to 48 hours

Ticket Link

Fixes #54

[mickmister]

LGTM 👍 just one comment suggestion

[larkox]

LGTM, just a small comment.

[codecov-io]

Codecov Report

Merging #82 into master will decrease coverage by 0.31%.
The diff coverage is 4.16%.

@@            Coverage Diff             @@
##           master      #82      +/-   ##
==========================================
- Coverage   28.20%   27.89%   -0.32%     
==========================================
  Files          57       58       +1     
  Lines        2053     2076      +23     
==========================================
  Hits          579      579              
- Misses       1409     1432      +23     
  Partials       65       65              

Impacted Files	Coverage Δ
server/command/subscribe.go	0.00% <0.00%> (ø)
server/jobs/renew_job.go	0.00% <0.00%> (ø)
server/mscalendar/subscription.go	0.00% <0.00%> (ø)
server/remote/msgraph/subscription.go	0.00% <ø> (ø)
server/jobs/job_manager.go	77.41% <100.00%> (ø)

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[mickmister]

/update-branch

[DHaussermann]

Spoke with @mickmister We want to merge this now to be verified in master. This will aid in making other PRs more testable.