[Renewal] Fix current authorization management for renewal - do not decrease authorization with renewal.

[bkontur]

Basically, when user is once authorized for 64 MiB (because he paid for that somewhere), we should all the time allow him to use full 64MiB. If he wants more, he needs to pay.

First issue:

Actually, we authorize user for 64 MiB, when uploads e.g 4MiB file, we decrease authorization to 64-4=60MiB, when he renews those 4MiB, we again decrease the authorization 60-4=56 MiB -> this something we should not do. The user still should be able to upload 60MiB.

Second issue:
Again, we authorize user for 64 MiB, when uploads e.g 4MiB file, we decrease authorization to 64-4=60MiB.
But now he does not renew, and after RetentionPeriod the 4MiB are removed, but user still has only 60MiB, we should return back those 4 MiB to the authorization.

TODO

• fix this renewal management
• make sure it is covered with tests
• (later) [Example] Renew functionality #104

[bkontur]

cc: @karolk91 this is orthogonal to the auto-renewal feature