Feature/225 swagger documentation

[RubenFricke]

Description

Improved swagger documentation by adding:

• Response codes for each endpoint
• Return model for each endpoint
• Description for each controller
• Description for the general swagger page

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• My code follows the style guidelines of this project
• I did not update API Controllers, if I did, I added/changed Postman tests
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I updated the changelog with an end-user readable description
• I assigned this pull request to the correct project board to update the sprint board

Steps to Test or Reproduce

Outline the steps to test or reproduce the PR here.
These steps will be used during release testing.

1. When you navigate to the swagger page, you should see below Dex API (below '/swagger/v1/swagger.json') a general description for the swagger page for Dex
2. After each controller name, there should be a small description visible for each controller individually
3. In a response tab, you should be able to see under 'Reponses' all the difference response codes with a short description, example value, schema, and media type.
4. All response media types should be set to application/json
5. All request media types should be set to application/json as the default value
6. When placing `[Consumes("")]' attribute for an endpoint, this endpoint won't be set to json automatically because you set your own custom configuration for the endpoint

Link to issue

Closes: #225

[jcoenen96]

Could you please end all the commentary with a dot? This should be in the syntax guidelines. I noticed a lot of existing commentary doesn't end with a dot either. Would be nice to have some consistency and have them all end with a dot.

[Brend-Smits]

@jcoenen96 and @StijnGroenen is this one good to go?