feat(users/Profpatsch/whatcd-resolver): trace http requests

Move the http calls into their own module, so we can trace the request
and provide a simple copy-to-replay command.

We have to work around a bug in the otel library, which would limit
our attribute value length to 128 bytes because it uses the wrong
option value.

~~~

`ifExists` is finally made more useful for dealing with optional
attributes in e.g. lists.

Change-Id: Iafab523e9ec4b00136db43f31fdc12aeefb7f77c
Reviewed-on: https://cl.tvl.fyi/c/depot/+/11241
Tested-by: BuildkiteCI
Autosubmit: Profpatsch <mail@profpatsch.de>
Reviewed-by: Profpatsch <mail@profpatsch.de>

users/Profpatsch/whatcd-resolver/src/Optional.hs

@@ -0,0 +1,18 @@
+module Optional where
+
+import GHC.Records (getField)
+import MyPrelude
+
+newtype Optional a = OptionalInternal (Maybe a)
+  deriving newtype (Functor)
+
+mkOptional :: a -> Optional a
+mkOptional defaultValue = OptionalInternal $ Just defaultValue
+
+defaults :: Optional a
+defaults = OptionalInternal Nothing
+
+instance HasField "withDefault" (Optional a) (a -> a) where
+  getField (OptionalInternal m) defaultValue = case m of
+    Nothing -> defaultValue
+    Just a -> a