use askama_actix responders so we get the correct content types/other headers for free

Cargo.lock

@@ -320,6 +320,17 @@ dependencies = [
  "askama_shared",
 ]
 
+[[package]]
+name = "askama_actix"
+version = "0.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c52f74f8382a142ecfc052100b21abc33f2c069e20fe345808e7ed914b179449"
+dependencies = [
+ "actix-web",
+ "askama",
+ "askama_shared",
+]
+
 [[package]]
 name = "askama_derive"
 version = "0.11.2"
@@ -1582,6 +1593,7 @@ dependencies = [
  "actix-web",
  "actix-web-actors",
  "askama",
+ "askama_actix",
  "bytes",
  "bytesize",
  "crc32fast",