feature: Add relationship between core entities to make it persistable in database

[shivasurya]

Description:

This PR adds relationship between the entities which should help to store them in relational format. Creating relationship between the entities reduces drastically search space to filter nodes while codeql query is executed. Further more adopting #190 class support further drives to implement class and filters by the end users to reduce the search space.

⚠️ One caveat I'm okay with is that if the end user crafts the query without relationship between entities will obviously trigger cartesian product and waste memory and computing time. We could warn the user by checking the cardinality of the dataset before filtering or generating cartesian product and let the user decide to run the query.

Checklist:

• Tests passing (gradle testGo)?
• Lint passing (golangci-lint run this requires golangci-lint)?

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1682 lines in your changes missing coverage. Please review.

Project coverage is 13.78%. Comparing base (ae4662a) to head (c2097d9).

Files with missing lines	Patch %	Lines
sourcecode-parser/tree/construct.go	0.00%	226 Missing ⚠️
sourcecode-parser/model/expr.go	0.00%	202 Missing ⚠️
sourcecode-parser/model/reftype.go	0.00%	187 Missing ⚠️
sourcecode-parser/tree/java/parse_expr.go	0.00%	175 Missing ⚠️
sourcecode-parser/model/member.go	0.00%	148 Missing ⚠️
sourcecode-parser/tree/java/parse_method.go	0.00%	137 Missing ⚠️
sourcecode-parser/db/db.go	0.00%	115 Missing ⚠️
sourcecode-parser/tree/query.go	0.00%	104 Missing ⚠️
sourcecode-parser/tree/java/parse_statement.go	0.00%	75 Missing ⚠️
sourcecode-parser/tree/java/parse_class.go	0.00%	68 Missing ⚠️
... and 12 more

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #195       +/-   ##
===========================================
- Coverage   72.42%   13.78%   -58.64%     
===========================================
  Files          16       30       +14     
  Lines        2473     2966      +493     
===========================================
- Hits         1791      409     -1382     
- Misses        639     2545     +1906     
+ Partials       43       12       -31     

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