Honor AWS_ENDPOINT_URL_<SERVICE> env vars in generated Erlang clients

[vulkoingim]

Depends on aws_beam_core:apply_endpoint_url_override

As a disclosure I have used a LLM to generate the code, but I have tested and verified that the generated erlang lib compiles and works against:

• DynamoDB Local with AWS_ENDPOINT_URL_DYNAMODB
• Real DynamoDB, no endpoint override
• RustFS with AWS_ENDPOINT_URL_S3
• Real S3

Generates do_request in the form:

 do_request(Client, Action, Input0, Options) ->
     Client1 = Client#{service => <<"dynamodb">>},
-    Host = build_host(<<"dynamodb">>, Client1),
-    URL = build_url(Host, Client1),
+    DefaultHost = build_host(<<"dynamodb">>, Client1),
+    {URL, Host} = aws_util:apply_endpoint_url_override(
+        build_url(DefaultHost, Client1), DefaultHost, <<"/">>,
+        <<"AWS_ENDPOINT_URL_DYNAMODB">>),
     Headers = [
         {<<"Host">>, Host},
         {<<"Content-Type">>, <<"application/x-amz-json-1.0">>},

Tested after generating the code, and patching the aws_util in aws-erlang.

cd aws-erlang
rebar3 compile
./test.escript
# and targeting local instances
export AWS_ENDPOINT_URL_S3=http://loclahost:9000
export AWS_ENDPOINT_URL_DYNAMODB=http://localhost:9001

#!/usr/bin/env escript
main(_) ->
    [code:add_pathz(E) || E <- filelib:wildcard("_build/default/lib/*/ebin")],
    {ok, _} = application:ensure_all_started(hackney),
    Env = fun(K) -> case os:getenv(K) of false -> halt(1); V -> list_to_binary(V) end end,
    Client = aws_client:make_client(Env("AWS_ACCESS_KEY_ID"), Env("AWS_SECRET_ACCESS_KEY"), Env("AWS_REGION")),
    io:format("DDB:  ~p~n", [aws_dynamodb:list_tables(Client, #{}, [])]),
    io:format("S3:   ~p~n", [aws_s3:list_buckets(Client, #{}, #{}, [])]).

[onno-vos-dev]

@vulkoingim I'll leave it up to you if you wanna address my comments. If I don't hear back from you by tomorrow, I'll merge it anyway but I think my comments would be cleaner. At least the obsolete util.ex code. Parsing these things is kinda brittle so the less places that deal with this sort of logic, the better.