Account for uploaded files in storage statistics

What does this MR do?

Up to now we have not been taking uploads into consideration for computing total storage usage for repositories. This changes that.

Database

Migrations

---

UP

== 20201105021637 AddUploadsSizeToProjectStatistics: migrating ================
-- add_column(:project_statistics, :uploads_size, :bigint, {:default=>0, :null=>false})
   -> 0.0191s
== 20201105021637 AddUploadsSizeToProjectStatistics: migrated (0.0192s) =======

== 20201105024127 AddUploadsSizeToNamespaceRootStorageStatistics: migrating ===
-- add_column(:namespace_root_storage_statistics, :uploads_size, :bigint, {:default=>0, :null=>false})
   -> 0.0017s
== 20201105024127 AddUploadsSizeToNamespaceRootStorageStatistics: migrated (0.0017s)

DOWN

== 20201105024127 AddUploadsSizeToNamespaceRootStorageStatistics: reverting ===
-- remove_column(:namespace_root_storage_statistics, :uploads_size)
   -> 0.0135s
== 20201105024127 AddUploadsSizeToNamespaceRootStorageStatistics: reverted (0.0135s)

== 20201105021637 AddUploadsSizeToProjectStatistics: reverting ================
-- remove_column(:project_statistics, :uploads_size)
   -> 0.0015s
== 20201105021637 AddUploadsSizeToProjectStatistics: reverted (0.0015s) =======

Queries

---

Sum of uploads in a project

Explain: https://explain.depesz.com/s/Vov3

Query

SELECT SUM("uploads"."size") FROM "uploads" WHERE "uploads"."model_id" = 278964 AND "uploads"."model_type" = 'Project'

Timings

Time: 1.460 s
  - planning: 0.167 ms
  - execution: 1.460 s
    - I/O read: 1.306 s
    - I/O write: 0.000 ms

Shared buffers:
  - hits: 6877 (~53.70 MiB) from the buffer pool
  - reads: 65484 (~511.60 MiB) from the OS file cache, including disk I/O
  - dirtied: 615 (~4.80 MiB)
  - writes: 0

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team

Related to #241980