add correct MIME Types to F-Droid.apk downloads

RewriteRule seems to default to text/html as the MIME Type.

closes web-services#31 (closed)

web-services!31 (merged)

I tested this on https://staging.f-droid.org/

 ~ $ curl --head https://staging.f-droid.org/F-Droid.apk.asc 

HTTP/1.1 200 OK
Date: Thu, 04 Apr 2024 10:17:49 GMT
Server: Apache/2.4.57 (Debian)
Last-Modified: Sat, 22 Jul 2023 19:25:37 GMT
ETag: "293-601185890ee40"
Accept-Ranges: bytes
Content-Length: 659
Content-Type: application/pgp-signature

 ~ $ curl --head https://staging.f-droid.org/F-Droid.apk

HTTP/1.1 200 OK
Date: Thu, 04 Apr 2024 10:17:53 GMT
Server: Apache/2.4.57 (Debian)
Last-Modified: Sat, 22 Jul 2023 19:25:37 GMT
ETag: "a2739e-601185890ee40"
Accept-Ranges: bytes
Content-Length: 10646430
Content-Type: application/vnd.android.package-archive