feat(docs): add customColumns to the docs-readme output target

[johnjenkins]

What is the current behavior?

GitHub Issue Number: N/A

What is the new behavior?

Lets consumers append custom columns to the generated readme.md Properties and Events tables, driven by arbitrary JSDoc tags.

Usage

Just say you want to flag props that are configurable via a global store/design-token system

// stencil.config.ts
export const config: Config = {
  outputTargets: [
    {
      type: 'docs-readme',
      customColumns: {
        props: [
          {
            header: 'Configurable',
            content: (prop) =>
              prop.docsTags.some((t) => t.name === 'config') ? '✅' : '❌',
          },
        ],
      },
    },
  ],
};

// my-component.tsx

/** @config */
@Prop() theme: string;

Results in

Property	Attribute	Description	Type	Default	Configurable
theme	theme		string	undefined	✅

Documentation

Does this introduce a breaking change?

• Yes
• No

Testing

Other information