feat: add TLS configuration support to Java SDK

[markphelps]

Summary

• Add comprehensive TLS configuration options to the Java client SDK, matching the functionality from the Python implementation
• Add TlsConfig class with builder pattern and static factory methods
• Support CA certificates (file paths and raw data), client certificates for mutual TLS, and insecure mode for development
• Update ClientOptions and FliptClient to accept TLS configuration
• Update tests to handle HTTPS URLs with TLS configuration automatically
• Add comprehensive README documentation with examples

cc @cristianonicolai

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 14 lines in your changes missing coverage. Please review.

Project coverage is 75.31%. Comparing base (f701007) to head (71da9df).
Report is 433 commits behind head on main.

Files with missing lines	Patch %	Lines
flipt-engine-ffi/src/http.rs	0.00%	10 Missing ⚠️
flipt-engine-ffi/src/lib.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1135      +/-   ##
==========================================
- Coverage   80.36%   75.31%   -5.05%     
==========================================
  Files           8        9       +1     
  Lines        4165     4477     +312     
==========================================
+ Hits         3347     3372      +25     
- Misses        818     1105     +287     

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[Copilot]

Pull Request Overview

This PR adds comprehensive TLS configuration support to the Java SDK as well as updates in related components and tests. Key changes include:

• Adding a new TlsConfig class (with builder and static factory methods) to support custom CA certificates and mutual TLS.
• Updating the FliptClient and ClientOptions in the Java SDK to accept TLS configuration.
• Enhancing tests (Go, Rust, and Python) and documentation to showcase and verify TLS setup.

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
test/main.go	Updated container configurations to mount TLS fixtures and set HTTPS environment variables.
flipt-engine-ffi/src/lib.rs	Modified TLS configuration usage with a fallback error handling mechanism for the fetcher builder.
flipt-engine-ffi/src/http.rs	Added a default implementation for HTTPFetcherBuilder.
flipt-client-python/flipt_client/models.py	Added certificate file validation using conditional Pydantic validators.
flipt-client-java/src/test/java/TestFliptClient.java	Added TLS configuration usage in test setup for secure connections.
flipt-client-java/src/main/java/io/flipt/client/models/TlsConfig.java	Introduced the new TlsConfig class implementing various TLS setup options.
flipt-client-java/src/main/java/io/flipt/client/models/ClientOptions.java	Extended ClientOptions to include TLS configuration.
flipt-client-java/src/main/java/io/flipt/client/FliptClient.java	Integrated TLS configuration into client instantiation and examples.
flipt-client-java/README.md	Updated documentation to include examples and explanations for TLS configuration.

[erka]

nice