Workshop fixes/improvements

- /!\ Add IMPORTANT note in azure to NOT use a company account as can enforce restrictive policies /!\
- Rewrite the env variable part: make command to set UNIQUE_ID explicit and tell Codespaces user they don't have to do anything.
- Use env.sh directly instead of copy/paste the commands
- Add note for how to run the load testing with jmeter locally
- preinstall graavlm in codespaces and provide the script for switching