[ApolloCodegen] Support for multiple headers

[LachlanMcCulloch]

Currently, in ApolloCodegen you can only initialize ApolloSchemaOptions with a single header property, which is translated to --header="<HEADER>". Since the Apollo CLI allows for multiple headers arguments (... --header=<HEADER1> --header=<HEADER2>), I was wondering if it would be possible to implement this in this tool?

One potential way, albeit a breaking change, is to do the following:

let headers: [String]
...
  public init(schemaFileName: String = "schema",
              schemaFileType: SchemaFileType = .json,
              apiKey: String? = nil,
              endpointURL: URL,
              headers: [String] = [],
              outputFolderURL: URL,
              downloadTimeout: Double = 30.0) {
    self.apiKey = apiKey
    self.headers = headers
    self.endpointURL = endpointURL
    self.outputURL = outputFolderURL.appendingPathComponent("\(schemaFileName).\(schemaFileType.rawValue)")
    	
    self.downloadTimeout = downloadTimeout
  }

...
for header in headers {
    arguments.append("--header='\(header)'")
}

This changes header to an array of headers instead and provides the same logic to append extra headers to the end of the CLI call.

I've tested this with a forked repo and it appears to still work, of course after updating any implementations to use headers, instead of header:
LachlanMcCulloch@fe5d417

Let me know if you need any more supporting information or clarification.

Cheers! :)

[designatednerd]

Yep this is exactly why this is still in Beta. 😃

Wanna open a PR?

[LachlanMcCulloch]

@designatednerd - sure can!
#1153

[designatednerd]

Awesome, thank you!

[LachlanMcCulloch]

Thanks @designatednerd 😄

[designatednerd]

This has shipped with 0.26.0!