Upgrades and improvements

• Upgraded Flink to 1.19.1 for compatibility with Python modules
• Added pyflink (Flink for python) as dependency in easybuild file
• Upgraded Spark to 3.5.3
• Added pyspark (Spark for python) as dependency in easybuild file The dependency already exists. So no need to add this.
• Simplified Makefile install-* target
• Added SITE_ID_TOKEN to the CI file. Source
• Added test case for Pylfink in CI file