Added support for multiple api keys in rust (reqwest)

[GeorgeFkd]

Relevant Context:

Issue #8833 and PR #8868

A more standard approach is followed here using a Map for Api Keys as seen in C# client example

API Key prefixes support was not added in this PR, can work on it here or a separate PR.

For the example(The Rock Trading public api) provided in #8833 the code of interest produced by the generator is:

if let Some(local_var_apikey) = local_var_configuration.api_keys.get("X-TRT-SIGN") {
   let local_var_key = local_var_apikey.clone();
   local_var_req_builder = local_var_req_builder.header("X-TRT-SIGN", local_var_key);
};
if let Some(local_var_apikey) = local_var_configuration.api_keys.get("X-TRT-KEY") {
   let local_var_key = local_var_apikey.clone();
   local_var_req_builder = local_var_req_builder.header("X-TRT-KEY", local_var_key);
};
if let Some(local_var_apikey) = local_var_configuration.api_keys.get("X-TRT-NONCE") {
   let local_var_key = local_var_apikey.clone();
   local_var_req_builder = local_var_req_builder.header("X-TRT-NONCE", local_var_key);
};

Rust Technical Comittee

cc @frol (2017/07) @farcaller (2017/08) @richardwhiuk (2019/07) @paladinzh (2020/05)

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[wing328]

thanks for the PR

but we can't merge it to master since it's a breaking change (users need to update their code accordingly to make it compile)

we need to do something like #20069

i will try to take care of it later.

thanks again for the work and sorry for the delay in getting it merged