build-enclave ignores Dockerfile ENTRYPOINT when CMD is present

[MatanHamilis]

In the following snippet:

aws-nitro-enclaves-cli/enclave_build/src/docker.rs

Lines 273 to 282 in 9758997

	if let Some(cmd) = &config.cmd {
	let env = config.env.unwrap_or_default();
	return Ok((cmd.clone(), env));
	}
	// If no CMD instructions are found, try to locate an ENTRYPOINT command
	if let Some(entrypoint) = &config.entrypoint {
	let env = config.env.unwrap_or_default();
	return Ok((entrypoint.clone(), env));
	}

The nitro-cli utility extracts the entrypoint of the resulting image being built.
It does so by:

1. Checking if a CMD command is present.
2. If not (and only in that case) it uses the ENTRYPOINT command.

This is incompatible with the Dockerfile reference (see CMD and ENTRYPOINT reference).

In particular it is stated that when an ENTRYPOINT is present, the CMD is merely set as a default set of arguments to the ENTRYPOINT.
For example:

If the user specifies arguments to docker run then they will override the default specified in CMD, but still use the default ENTRYPOINT.

I think an expected behavior would be the equivalent of running docker run which is the concatenation of ENTRYPOINT (if present) with CMD (if present). If none exists, one should probably just run the default login shell.