enable mixed content in the API pages directory

[thescientist13]

Summary

Coming out of #955 / #1212, one follow up item was that after the change to collapsing down the API directory into the page directory, instead of being its own top level directory

src/
  pages/
    api/
      search.js   

A question of mixed content came up as a discussion around that topic, which basically came down to, what if you actually wanted pages in that directory? Like for actual API documentation.

src/
  pages/
    api/
      index.html  

Details

So we could easily support this for static pages, e.g. markdown and HTML, just like we detect normal pages. But what happens if you actually wanted a server / pre-rendered page, like say for building up a table of contents, or auto generating docs, e.g.

// src/pages/api/index.js
import fs from 'fs/promises';

export default class ApiDocsPage extends HTMLElement {

  connectedCallback() {
    // could also come through the graph as constructor props
    const pages = await fs.promises.readDir('./.').filter(file => file.split('.').pop() === 'md'));

    this.innerHTML = `
      <h1>Table of Contents</h1>
        <nav>
          <ol>
            ${ 
              pages.map((page) => {
                const name = page.replace('.md', '');

                return `<li><a href="/${name}/">${name}</a></li>`; 
              }).join('')
            }
         </ol>
       </nav>
     `;
   }
}

How would / could Greenwood specifically detect this case vs just any other API route? Basically, have Greenwood support all these use cases at once

src/
  pages/
    api/
      search.js // classic API route
      index.html // static page
      docs.js // SSR page

---

Most naive approach could be to just have SSR pages in the API directory export a flag, which we already support?

https://www.greenwoodjs.io/docs/server-rendering/#prerender
export const prerender = true;

// or

export const ssr = true;