Add endpoint to fetch filters in JSON format

[jchristgit]

While this is an API endpoint consumed by the bot, keep it in the
resources app instead of the api app, as all the logic and data for
resources is contained within the resources app and we don't want to
start messing around with that.

The response format from the endpoint is as follows:

{
    "topics": [
        "algorithms-and-data-structures",
        "data-science",
        "databases",
        "discord-bots",
        "game-development",
        "general",
        "microcontrollers",
        "security",
        "software-design",
        "testing",
        "tooling",
        "user-interface",
        "web-development",
        "other"
    ],
    "payment_tiers": [
        "free",
        "paid",
        "subscription"
    ],
    "type": [
        "book",
        "community",
        "course",
        "interactive",
        "podcast",
        "project-ideas",
        "tool",
        "tutorial",
        "video"
    ],
    "difficulty": [
        "beginner",
        "intermediate"
    ]
}

Closes #710.

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[coveralls]

coverage: 100.0%. remained the same
when pulling c63ab0b on resource-filter-fetch
into e51d80a on main.

[wookie184]

The response format here doesn't seem ideal. My understanding is that "filters" is the display name, and "valid_filters" is what goes in the URL(?), but the response doesn't link these together.

We could link them together in the structure, along the lines of this:

[
    {
      "name": "Difficulty",
      "query_param": "difficulty",
      "options": [
        {"name": "Beginner", "query_value": "beginner"},
        ...
      ],
      "icon": "fas fa-brain",
      "hidden": false,
    },
    ...
]

Alternatively we could maybe just drop the "valid_filters" section and document the transformation to get from the name to the url.

[jchristgit]

@wookie184 thanks for the review and sorry for the long delay. I've updated the response format, the "sluggified" / "kebabified" version of the names can now be found in the slug field for the respective category, and the filter_slugs field for each filter. To be specific, filter_slugs[3] == to_kebabcase(slugs[3]). Let me know what you think.

[wookie184]

This seems to undo the fix for #1209, I think it will cause performance issues.

[jchristgit]

Looks like I managed to mess up during rebasing. It should all be fine now, and the code should be a lot simpler thanks to Rohan's changes. Please also see the new response file format.