Add stdout output definition for tfsec command in entrypoint.sh

[rbrasco]

Currently, this GitHub Action lacks the output variable for capturing the stdout output of the tfsec command. To enhance the utility and provide more detailed feedback to users, I propose adding the following code snippet to the entrypoint.sh script. This addition will capture the stdout of the tfsec execution and define it as tfsec-stdout, making it available in the GitHub Action's output. Being TFSEC_OUTPUT the output of said command.

Proposed code addition:

{
  echo "tfsec-stdout<<EOF"
  echo "${TFSEC_OUTPUT}"
  echo "EOF"
} >> $GITHUB_OUTPUT