feat: add configurable issue url

[sempostma]

Summary

A small change that makes the issue url configurable.

In my case, I need this since my client is non-technical. Redirecting them to a Github issue page will just confuse them. A custom url will allow for creating a custom endpoint for automatic reporting of issues.

[martinjagodic]

Great idea @sempostma.

Please also add this to the schemas, as it is a new config field. These files all generate a schema (don't ask me why there's 3):

• packages/decap-cms-core/index.d.ts
• packages/decap-cms-core/src/constants/configSchema.js
• packages/decap-cms-core/src/types/redux.ts

We will also need a PR on the docs site that documents the new option. I think we should put it above Collections on https://decapcms.org/docs/configuration-options/

[sempostma]

I've updated the schema and added a PR for the docs: decaporg/decap-website#152

[sempostma]

@martinjagodic Rebased on the main branch to fix the minimatch error.

[yanthomasdev]

Code LGTM, I'll review the docs next, appreciate the contribution 🙌

[martinjagodic]

@sempostma, please run npm run format so tests will pass. thanks!

[martinjagodic]

Thanks. I am fixing tests in another PR. When it's merged, this one follows soon after