script type="module" support

[simonw]

Custom JavaScript can be loaded in metadata.json like this:

{
    "extra_js_urls": [
        {
            "url": "https://code.jquery.com/jquery-3.2.1.slim.min.js",
            "sri": "sha256-k2WSCIexGzOj3Euiig+TlR8gA0EmPjuc79OEeY5L45g="
        }
    ]
}

Add a "module": true option which causes the resulting script element to use <script type="module">

[simonw]

Updated documentation: https://docs.datasette.io/en/latest/custom_templates.html#custom-css-and-javascript and https://docs.datasette.io/en/latest/plugin_hooks.html#extra-js-urls-template-database-table-columns-view-name-request-datasette