Add compiler validations for custom foreign key fields

[hasathcharu]

Purpose

To support the newly added sql:Relation annotation to allow definition of custom foreign keys.

Fixes: ballerina-platform/ballerina-library/issues/6068

Checklist

• Linked to an issue
• Updated the specification
• Updated the changelog
• Added tests
• Checked native-image compatibility

[codecov]

Codecov Report

Attention: Patch coverage is 57.44681% with 20 lines in your changes are missing coverage. Please review.

Project coverage is 87.09%. Comparing base (02872be) to head (ac75229).

Files	Patch %	Lines
...ballerina/stdlib/persist/compiler/utils/Utils.java	5.55%	16 Missing and 1 partial ⚠️
...sist/compiler/PersistModelDefinitionValidator.java	94.73%	0 Missing and 1 partial ⚠️
...allerina/stdlib/persist/compiler/model/Entity.java	66.66%	1 Missing ⚠️
...stdlib/persist/compiler/model/SimpleTypeField.java	66.66%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #274      +/-   ##
============================================
- Coverage     88.49%   87.09%   -1.41%     
- Complexity      343      346       +3     
============================================
  Files            30       30              
  Lines          1113     1147      +34     
  Branches        135      141       +6     
============================================
+ Hits            985      999      +14     
- Misses           76       94      +18     
- Partials         52       54       +2     

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[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

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

See analysis details on SonarCloud