[Core] Inform user if bash too old for shell completion

[jucor]

As discussed in #3885.

I extend the bash command that installs the shell completion to explain to the user that their bash is too old, if the version check added in #2433 fails.

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below) not needed
• All smoke tests: pytest tests/test_smoke.py none relevant
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name none relevant
• Backward compatibility tests: conda deactivate; bash -i tests/backward_compatibility_tests.sh not relevant

[Michaelvll]

Thanks for adding the error message @jucor! LGTM.