Add more helpful error messages for KeyError

[caizixian]

[INFO] 2024-08-06 06:29:57,770 minheap.py:190 Temporary directory: /tmp/minheap-9i51vtq5
Traceback (most recent call last):
  File "/usr/local/bin/running", line 8, in <module>
    sys.exit(main())
  File "/usr/local/lib/python3.10/dist-packages/running/__main__.py", line 50, in main
    if m.run(args):
  File "/usr/local/lib/python3.10/dist-packages/running/command/minheap.py", line 192, in run
    run_with_persistence(result, Path(minheap_dir), None, attempts)
  File "/usr/local/lib/python3.10/dist-packages/running/command/minheap.py", line 115, in run_with_persistence
    runtime, mods = parse_config_str(configuration, c)
  File "/usr/local/lib/python3.10/dist-packages/running/util.py", line 68, in parse_config_str
    runtime = configuration.get("runtimes")[c.split("|")[0].strip()]
KeyError: 'jdk21'

Should tell the user which part of the config that the lookup happened.