`eic_curl_authorized_keys` returns incorrect exit code in some cases

In [this section of the code](https://github.com/aws/aws-ec2-instance-connect-config/blob/1.1.17/src/bin/eic_curl_authorized_keys#L89-L95) `curl` is called with `-f` which causes it to return exit code 22 when the HTTP response code is >= `400`. This means that when the user doesn't have any keys for example, and the metadata service returns `404`, the script exits with code `22` due to the `set -e` in the script.

I discovered this when calling `eic_run_authorized_keys` as an additional fallback for my `AuthorizedKeysCommand` script, I was executing:

```
exec /usr/share/ec2-instance-connect/eic_run_authorized_keys "${@}"
```

Which would then cause my own script to return exit code 22, and thus no keys produced by the calling script were accepted at all either due to the non-zero code.

I am filing a bug because the logic in the script shows an intention for this to be an `exit 0` scenario.

Start with src/bin/eic_curl_authorized_keys around lines 89-95 and inspect how the curl 404 case interacts with set -e. Reproduce the no-keys metadata response, then verify that the authorized-keys command returns exit 0 while preserving the expected behavior for successful responses.

Written by the indexing model from the issue text.