[Feature] Support flag auto add UIDs to Entities and Properties

[dyno-nexsoft]

When build_runner i want auto to add uid to @entity and @Property to data model.
For fix conflict and rollback file better.

Doc https://docs.objectbox.io/advanced/data-model-updates#how-to-and-example-java-kotlin-and-dart
Repeating those steps is too time consuming.

[greenrobot-team]

Thanks for the suggestion! Out of curiousity, why would you want to add UIDs to presumably all entities and properties? This is typically not needed, unless for ex. renaming the classes or fields.

[dyno-nexsoft]

Fixing conflicts on json files is difficult to control. So I want to easily track the class before and after merging and how the field will be changed. Because my team can easily get confused when fixing between many branches on JSON files.