Add dataset size limits

[HeDo88TH]

This PR closes #31 by adding the support for maxStorageMB user metadata.
New configuration key EnableStorageLimiter to enable this limiter, if false it does not check the user's available storage space.
New endpoint GET /users/storage it returns the current user's storage info:

{
  "total": 314572800,
  "used": 307377818
}

When the user goes beyong its quota a new MaxUserStorageException is thrown.

[HeDo88TH]

In Hub we need to change the behaviour of Share because It keeps retrying even after server error for quota exceeded, tracked in DroneDB/Hub#47

[pierotofy]

We should at least memoize this. https://github.com/eirikt/Memoizer.NET

It's OK if we allow a user to exceed its quota, for a brief period of time, so long as at a certain point we detect that the quota has exceeded and we can take action.

[HeDo88TH]

Very cool library, check #191 (comment)

[HeDo88TH]

I performed some empirical tests on my machine. I tested from 1 to 200 datasets the wait time after the new file upload.
I'm using the cached S3 configuration. The wait times are per file upload.

Datasets	Wait time (s)
1	0,18
5	0,20
10	0,28
20	0,46
30	0,52
40	0,69
50	0,76
75	1,02
100	1,40
150	2,01
200	2,40

There is definitely a linear correlation between the wait time and the number of datasets.
We can optimize this but I do not think that it is high on our priority list @pierotofy

[pierotofy]

🐢

[pierotofy]

I would add this right away, but you decide. It will take more work later imo.

[HeDo88TH]

I would add this right away, but you decide. It will take more work later imo.

Tracked in #192

[pierotofy]

Works good for share and file upload endpoint.

I found an issue with ddb push though;

If I clone an empty repository, add lots of files (past my storage limit), then ddb push, the first ddb push succeeds. Subsequent attempts to push fail with the correct message, but the first one seems to go unchecked.

To reproduce:

ddb clone <dataset>
cd <dataset>
ddb add [files adding to the storage limit for my user]
ddb push
--> succeeds (incorrect)
ddb add [another file]
ddb push
--> fails (correct)

[HeDo88TH]

Works good for share and file upload endpoint.

I found an issue with ddb push though;

If I clone an empty repository, add lots of files (past my storage limit), then ddb push, the first ddb push succeeds. Subsequent attempts to push fail with the correct message, but the first one seems to go unchecked.

Fixed in 8f3a3d1
Basically we now check in push upload endpoint and not in init, this way the user can push an "all delete" without getting blocked if he has gone beyond its quota BUT he gets blocked if uploads new files.

[HeDo88TH]

Improvements tracked in #192
@pierotofy can we merge this?

[pierotofy]

Looks good. Thanks!