Badge Request: HTTP Last-Modified

### 📋 Description

It should show a human-readable date based on the HTTP Last-Modified header of an arbitrary URL, formatted similar to [GitHub last commit](https://shields.io/badges/git-hub-last-commit-branch). There would be no path parameters, and the query parameters would be the same as for GitHub last commit, with the addition of a `url` parameter, similar to [Security Headers](https://shields.io/badges/security-headers-dont-follow-redirects).

### 🔗 Data

Use a HEAD HTTP request (instead of GET, to cut down on bandwidth) and parse the Last-Modified header in the response.

### 🎤 Motivation

As an example use case, the [Tranco top 1M websites list](https://tranco-list.eu/) provides the timestamp of the daily updates in the Last Modified header. A project that uses the daily updates would benefit from including a badge that confirms when the last update to this dataset occurred.

But this is probably widely useful for many other use cases.

To clarify, AFAIK this is different than [Security Headers](https://shields.io/badges/security-headers-dont-follow-redirects) since that only shows problems with security-related HTTP headers, while this would show a badge based on Last-Modified header.

No repository files or tests are named. Start by locating the existing GitHub last commit and Security Headers badge entry points, then review their query-parameter and HTTP-request patterns; done means a badge accepts a url parameter, uses HEAD, parses Last-Modified, and supports the stated formatting options.

Written by the indexing model from the issue text.