Add zappr integration for better quality control

[OGKevin]

The purpose of this issue is to introduce https://zappr.opensource.zalan.do so that quality control on pull requests can be assured.

The following configuration should be used:

autobranch:
  pattern: 'bunq/sdk_csharp#{number}-{title}'
  length: 100
commit:
  message:
    patterns:
      - '([A-Za-z0-9 ]+)\. (\(bunq\/sdk_csharp#[0-9]+\))'
specification:
  title:
    minimum-length:
      enabled: true
      length: 8
  body:
    minimum-length:
      enabled: true
      length: 8
    contains-url: true
    contains-issue-number: true
  template:
    differs-from-body: true
pull-request:
  labels:
    additional: true
    required:
      - Reviewed by André
      - Can be merged