fix: Env manifest UX fix for http config

[paragbhingre]

This PR fix multiple problems -

1. This PR fix the env manifest fields that were organized in incorrect manner.
2. Also resolves #4032
3. copilot env init with private subnets create env manifest with following field

http:
  private:

This should only be created when there is at least one parameter inside private is enabled. This PR fix this nit as well.

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