feat(actix-files): support multiple fallback directory indexes

[imgurbot12]

PR Type

Feature / Refactor

PR Checklist

• Tests for the changes have been added / updated.
• Documentation comments have been added / updated.
• A changelog entry has been made for the appropriate packages.
• Format code with the latest stable rustfmt.
• (Team) Label with affected crates and semver status.

Overview

This modification allows for the support of multiple index file fallbacks, similar to apache2/nginx.
Eg. [index.actix.html, index.html, index.txt, ...]

The implementation appends the indexes to a vector rather than the default option, and is configured
using the existing Files::index_file which can be called multiple times to append each entry.

This design should avoid any breaking changes as the default behavior of just calling it once results in the same functionality before the modification.

This PR supports a personal project of mine attempting to implement an caddy/apache-style reverse-proxy service. Supported by a bunch of services I've written recently.

Thank you :)

[imgurbot12]

Is it possible to re-run the jobs on this one? It looks like some unrelated h2 unit-test timed out after getting stuck for almost an hour lol.