[GEN-868] add year death validation

[danlu1]

Problem:

Lack of validation check on whether YEAR_DEATH >= YEAR_CONTACT

Solution:

Add the validation check to compare YEAR_DEATH and YEAR_CONTACT when both of them exist and not NAs.

Testing: Unit test has been added.

[danlu1]

Thanks for doing this! Just some initial comments.

Edit: Could you add more details to the PR description?

Will do

[sonarcloud[bot]]

Quality Gate passed

Issues
20 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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