Compress NAR listings using the "text-compression" method

So if "text-compression=br", the .ls file in S3 will get a
Content-Encoding of "br". Brotli appears to compress better than xz
for this kind of file and is natively supported by browsers.

src/libstore/binary-cache-store.cc

@@ -224,7 +224,7 @@ void BinaryCacheStore::addToStore(const ValidPathInfo & info, const ref<std::str
             }
         }
 
-        upsertFile(storePathToHash(info.path) + ".ls.xz", *compress("xz", jsonOut.str()), "application/x-nix-nar-listing");
+        upsertFile(storePathToHash(info.path) + ".ls", jsonOut.str(), "application/json");
     }
 
     else {

src/libstore/s3-binary-cache-store.cc

@@ -267,9 +267,9 @@ struct S3BinaryCacheStoreImpl : public S3BinaryCacheStore
     void upsertFile(const std::string & path, const std::string & data,
         const std::string & mimeType) override
     {
-        if (path.find(".narinfo") != std::string::npos)
+        if (textCompression != "" && (hasSuffix(path, ".narinfo") || hasSuffix(path, ".ls")))
             uploadFile(path, *compress(textCompression, data), mimeType, textCompression);
-        else if (path.find("/log") != std::string::npos)
+        else if (logCompression != "" && hasPrefix(path, "log/"))
             uploadFile(path, *compress(logCompression, data), mimeType, logCompression);
         else
             uploadFile(path, data, mimeType, "");