CLI: Accept mulitple node identifiers in `verdi node graph generate`

[sphuber]

Fixes #3232

The --identifier option allows the user to specify which identifier to label nodes in the graph with: pk, uuid or label. Here, the interface is updated to allow specifying multiple identifiers, e.g.:

verdi node graph generate --identifier pk uuid -- <PK>

If more than one identifier type is specified, the resulting identifiers for each node are joined using a | character.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 81.81818% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 77.70%. Comparing base (ef60b66) to head (a3aee70). Report is 20 commits behind head on main.

Files	Patch %	Lines
src/aiida/tools/visualization/graph.py	77.78%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6443 +/- ## ========================================== + Coverage 77.51% 77.70% +0.20% ========================================== Files 560 562 +2 Lines 41444 41721 +277 ========================================== + Hits 32120 32415 +295 + Misses 9324 9306 -18 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.