Test getting the complete request URL

[jwodder]

For #179, the web view will need to be aware of what domain, port, and scheme (and possibly also URL path) the user is accessing dandidav at so it can display the same in the download instructions. This PR is a test of various ways to get this information. Performing the test involves merging & deploying this PR, accessing https://webdav.dandiarchive.org/.test and https://dandi.centerforopenneuroscience.org/.test, noting down the responses, and then deploying a new PR to revert this one.

For the record, when running dandidav locally with the default options, accessing http://localhost:8080/.test in Safari gives the response:

Host: localhost:8080
Original URI: /.test
Request URI: /.test
Headers:
  host: "localhost:8080"
  sec-fetch-site: "none"
  connection: "keep-alive"
  upgrade-insecure-requests: "1"
  sec-fetch-mode: "navigate"
  accept: "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
  user-agent: "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/17.5 Safari/605.1.15"
  accept-language: "en-US,en;q=0.9"
  sec-fetch-dest: "document"
  accept-encoding: "gzip, deflate"

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 16 lines in your changes missing coverage. Please review.

Project coverage is 46.15%. Comparing base (66c94eb) to head (138b84c).
Report is 2 commits behind head on main.

Files	Patch %	Lines
src/main.rs	0.00%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #180      +/-   ##
==========================================
- Coverage   46.33%   46.15%   -0.19%     
==========================================
  Files          29       29              
  Lines        3984     4000      +16     
==========================================
  Hits         1846     1846              
- Misses       2138     2154      +16     

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