fix: Fixes usage with eks pod identity

[amardatar]

Proposed changes

Fixes #373

This adds an additional branch to the entrypoint which checks for AWS_CONTAINER_AUTHORIZATION_FILE (in the same position as this check occurs in awscredentials.js) to prevent the script from failing when using EKS Pod Identities.

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[github-actions]

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[amardatar]

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[amardatar]

For reference - I've tested changes by building and running this image in my env.

[luhkevin]

Note - you should also add

env AWS_CONTAINER_CREDENTIALS_FULL_URI;
env AWS_CONTAINER_AUTHORIZATION_TOKEN_FILE;

to common/etc/nginx/nginx.conf in order to preserve these variables for worker threads.
Actually I'm not sure if AWS_CONTAINER_CREDENTIALS_FULL_URI is needed but AWS_CONTAINER_AUTHORIZATION_TOKEN_FILE is at least used when we read credentials via pod identity.