Process client age range from external submission

[martha]

Please squash merge this PR

Description

GH issue: https://github.com/open-path/Green-River/issues/6731

This PR adds processing for the age range field from PIT submissions. If a precise DOB is provided, that should always take precedence.

Type of change

• [ ] Bug fix
• [x] New feature (adds functionality)
• [ ] Code clean-up / housekeeping
• [ ] Dependency update

Checklist before requesting review

• [x] I have performed a self-review of my code
• [x] I have run the code that is being changed under ideal conditions, and it doesn't fail
• [x] My code includes comments and/or descriptive variable names to help other engineers understand the intent (or not applicable)
• [x] My code follows the style guidelines of this project (rubocop)
• [x] I have updated the documentation (or not applicable)
• [x] If it's not obvious how to test this change, I have provided testing instructions in this PR or the related issue