Add Override Response Headers field to Add API Backend form

[brylie]

The "Override Response Headers" field is not currently available on the Add API Backend form. This is inconsistent with the API Umbrella system.

Help text should read:

Define header values that will be set in the response regardless of whether the header is already set in the response.

For example, to force CORS headers on all responses:

Access-Control-Allow-Origin: *

Task

Verify existing field in API Umbrella

• Verify "Default Response Headers" field design on API Umbrella API Backend form
• Make note of field design, location on form, etc

Implement field in Apinf

• Update ApiBackends schema to include "Override Response Headers" field
• Ensure schema definition matches API Umbrella field name and validation settings
• Add field to Add API Backend form

Test new field

• Manually test that form submits both with and without field input
  • Ensure that submitted data is present in API Umbrella, i.e. that it validates

[bajiat]

@mauriciovieira I checked your task estimations for sprint 14 and it is about 25 hours. You estimated your availability as 49 hours. Some of that time will go to reviewing PR's, but would it also be possible for you to take tasks #504 and #503?

[brylie]

Co-pilot: @elnzv

[jykae]

Will this actually reset whatever there is in Response Headers? Could CORS header only be added to the set? Issue created with question NREL/api-umbrella#186