feat: json schema for access rules

[imrushi]

This adds schema validation for access rules. It will be useful for users and developers to take action prior to deploying the configuration to the Oathkeeper in order to verify the schema's rules and some of the validation in their IDE. It follows the Access Rule format.

Related issue(s)

Related to issue: #828

Checklist

• I have read the contributing guidelines.
• I have referenced an issue containing the design document if my change
  introduces a new feature.
• I am following the
  contributing code guidelines.
• I have read the security policy.
• I confirm that this pull request does not address a security
  vulnerability. If this pull request addresses a security vulnerability, I
  confirm that I got the approval (please contact
  security@ory.sh) from the maintainers to push
  the changes.
• I have added tests that prove my fix is effective or that my feature
  works.
• I have added or changed the documentation.

Further Comments

I'm not sure if I should add this schema to version.schema.json. 

[codecov]

Codecov Report

Merging #1074 (60c40da) into master (461f088) will increase coverage by 0.57%.
Report is 1 commits behind head on master.
The diff coverage is n/a.

❗ Current head 60c40da differs from pull request most recent head 551dee2. Consider uploading reports for the commit 551dee2 to get more accurate results

@@            Coverage Diff             @@
##           master    #1074      +/-   ##
==========================================
+ Coverage   77.65%   78.22%   +0.57%     
==========================================
  Files          79       80       +1     
  Lines        3979     3863     -116     
==========================================
- Hits         3090     3022      -68     
+ Misses        608      566      -42     
+ Partials      281      275       -6     

see 2 files with indirect coverage changes