Refactor and enhance template system handling

[kpavlov]

Made SystemMessageProvider a functional interface and added a default implementation for apply.

Introduced java examples on how to use templates for system and user prompts. Updated documentation and examples to simplify prompt template handling. Configured Maven for Kotlin and Java interop while adding proper compiler settings. Added Java sample demonstrating template usage.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.08% (target: -1.00%)	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (4ad0b2b)	191	154	80.63%
Head commit (dfb8136)	197 (+6)	159 (+5)	80.71% (+0.08%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#63)	7	7	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.75%. Comparing base (4ad0b2b) to head (dfb8136).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #63      +/-   ##
==========================================
+ Coverage   75.52%   75.75%   +0.23%     
==========================================
  Files          15       16       +1     
  Lines         192      198       +6     
  Branches       15       15              
==========================================
+ Hits          145      150       +5     
- Misses         38       39       +1     
  Partials        9        9              

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