[go-experimental] Support aliasing of API keys

Created by: jirikuncar

Support aliasing of API keys so users of generated clients don't have to specify same value under different names.

Example:

components:
  securitySchemes:
    apiKeyAuth:
      type: apiKey
      name: api_key
      in: query
      description: API Key
    apiKeyAuthHeader:
      type: apiKey
      name: SECURITY-API-KEY
      x-auth-id-alias: apiKeyAuth
      in: header
      description: API Key

One can also alias both names for compatibility reasons or simply nicer usage:

components:
  securitySchemes:
    apiKeyAuth:
      type: apiKey
      name: api_key
      x-auth-id-alias: secret
      in: query
      description: API Key
    apiKeyAuthHeader:
      type: apiKey
      name: SECURITY-API-KEY
      x-auth-id-alias: secret
      in: header
      description: API Key

PR checklist

• Read the contribution guidelines.
• If contributing template-only or documentation-only changes which will change sample output, build the project before.
• Run the shell script(s) under ./bin/ (or Windows batch scripts under.\bin\windows) to update Petstore samples related to your fix. This is important, as CI jobs will verify all generator outputs of your HEAD commit, and these must match the expectations made by your contribution. You only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the code or mustache templates for a language ({LANG}) (e.g. php, ruby, python, etc).
• File the PR against the correct branch: master, 4.3.x, 5.0.x. Default: master.
• Copy the technical committee to review the pull request if your PR is targeting a particular programming language.

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