l2sm-operator: cleaned python image

Following the python guidelines of usage, the operator's Dockerfile has been updated, to use a requirements.txt outside the dockerfile.

Identation fixes

build/build_images.sh

 #!/bin/bash
+set -e
 
 # Set environment variables
 export VERSION="2.2"

build/operator/Dockerfile

 FROM python:3.11.6
-RUN pip install kopf kubernetes PyMySQL cryptography requests
-COPY ./src/operator/l2sm-operator.py /l2sm-operator.py
-CMD kopf run --standalone --all-namespaces /l2sm-operator.py
+
+WORKDIR /usr/src/app
+
+COPY ./src/operator/requirements.txt ./
+RUN pip install --no-cache-dir -r requirements.txt
+
+COPY ./src/operator/l2sm-operator.py .
+
+CMD kopf run --liveness=http://0.0.0.0:8080/healthz --standalone --all-namespaces ./l2sm-operator.py

src/operator/requirements.txt

+kopf==1.37.0
+kubernetes==28.1.0
+PyMySQL==1.1.0
+cryptography==3.4.8
+requests==2.25.1
\ No newline at end of file