Add efficient concatenation of StructArrays

[asubiotto]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

We have observed excessive memory usage because StructArray concatenation falls back to concat_fallback which results in not merging nested dictionaries.

Describe the solution you'd like

Adding a concat_structs function to `concat.rs

Describe alternatives you've considered

Additional context

[alamb]

label_issue.py automatically added labels {'arrow'} from #7517