[BUG] Integer overflow on postgres evidences table

**Describe the bug**
The `file_size` field in evidence table is a POSTGRES integer, hence limited to 2 147 483 647 (~2GB). Issuing a request with a file_size above this, creates a HTTP 500 error. 

**Expected behavior**
Accept any file size.

**Additional context**
Moving to bigint will solve the issue for the next fews years : 9223372036854775807 max (~8192 pebibytes)
