Add mode to OPA format to migrate to strict mode complaint code

[ashutosh-narkar]

In OPA 1.0, some of the strict mode checks will be enabled by default. See #6271 for details. Also with the planned introduction of the rego.v1 import, some constraints will be introduced on the module. In order to help policy authors smoothly transition their existing policies to be compliant with these new changes, we could add a new flag to the opa fmt command to enable this. Ideally we should add this feature before the 1.0 release to help make the transition easier.

[ashutosh-narkar]

In OPA 1.0, a new annotation called additional-annotations will be introduced that will allow users to define custom data outside the custom attribute. opa fmt should annotate modules with this new annotation for cases where custom annotations are defined outside the “custom” block. We can add a new flag to opa fmt called --move-additional-annotations that users can use to move user-defined data under the “custom” block.