Vapor: 4.54.0 Release

This patch was authored by @NeedleInAJayStack and released by @0xTim.

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Many HTTP servers support specifying a default file when a request hits a public directory. For example, a request to http://server.com/path/ may automatically serve the file at path/index.html.

This PR adds this functionality to the FileMiddleware via an initialization parameter. It defaults to disabled but can be customized to whatever default file name is desired. This default file name is also served automatically for all subdirectory queries. If the default file does not exist, the request is passed on to the next Responder.

A usage example:

// Default file serving is disabled
app.middleware.use(FileMiddleware(publicDirectory: "public/"))

// Serves `index.html` (if it exists) to a request to `http://server.com/`, as well as any subdirectories
app.middleware.use(FileMiddleware(publicDirectory: "public/", defaultFile: "index.html"))

Resolves: https://github.com/vapor/vapor/issues/2455

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