Replace "result_vote_allow" with "view_results"

Problem/Motivation

result_vote_allow really seems like a strange key for an indication if you can view the poll results or not. It looks like a plain copy paste from the cancel_vote_allow field. Since we're working on a new major version we can deprecate this field and replace it with a better name. While doing this we can also update all getters and setters.

Proposed resolution

Field name suggestion: view_results or view_results_allow so it matches cancel_vote_allow.

- Create a new field
- Provide upgrade path
- Provide update hook to install new field and drop the old one after the data has been moved
- Deprecate the getters and setters on 8.x branch
- Add new getter and setters
- Update the draft release note to include this change

Remaining tasks

MR

User interface changes

N/A

API changes

New getters and setters.

Data model changes

New database field