TRUNK-6081: Add not null constraint to encounter_diagnosis.dx_rank

[wikumChamith]

Description of what I changed

Jave field Diagnosis.rank is marked as not nullable via the JPA annotations but encounter_diagnosis.dx_rank column is missing the not null constraint in the database. So this adds not null constraint to encounter_diagnosis.dx_rank column.

Issue I worked on

https://issues.openmrs.org/browse/TRUNK-6081

Checklist: I completed these to help reviewers :)

• [x] My IDE is configured to follow the code style of this project.

  No? Unsure? -> configure your IDE, format the code and add the changes with git add . && git commit --amend

• [ ] I have added tests to cover my changes. (If you refactored existing code that was well tested you do not have to add tests)

  No? -> write tests and add them to this commit git add . && git commit --amend

• [x] I ran mvn clean package right before creating this pull request and added all formatting changes to my commit.

  No? -> execute above command

• [x] All new and existing tests passed.

  No? -> figure out why and add the fix to your commit. It is your responsibility to make sure your code works.

• [x] My pull request is based on the latest changes of the master branch.

  No? Unsure? -> execute command git pull --rebase upstream master

[wikumChamith]

@wluyima I added a comment to describe the changeset.

[wikumChamith]

@wluyima Are there any additional changes I should make in this PR??

[wluyima]

Looks good

[wikumChamith]

New PR: https://github.com/openmrs/openmrs-core/pull/4199