support templating languages: `gohtml`

[grouville]

With the new emergence of htmx, no extension currently handles perfectly the htmx data extension on VSCode because the customData field is not extendable on those templating languages, even though we are writing a lot of HTML inside.

In a package.json, I would expect this to work:

    "contributes": {
        "html": {
            "customData": [
                "./html.htmx-data.json"
            ]
        },
        "gohtml": {
            "customData": [
                "./html.htmx-data.json"
            ]
        }
    }

Empirical tests on my fork of a fully working extension for html files: https://github.com/otovo/htmx-tags/compare/main...grouville:htmx-tags:main show that it does not