feat: Add HTTP credential exposure warnings

[stenalpjolly]

Context

This PR brings the Java SDK into parity with the Python and Go SDKs by introducing warnings for potential HTTP credential exposure.

Changes

• Client Initialization: Added credential exposure checks during client setup.
• Tool Loading: Implemented validation when loading tools to warn against insecure HTTP usage with credentials.
• Tool Invocation: Added runtime checks during tool execution to ensure credentials are not inadvertently exposed over unencrypted HTTP connections.
• Case-Insensitive Checks: Ensured all header and scheme validations are case-insensitive for robustness.

Design Considerations

• Clean Interface: Maintained a clean public interface without cluttering existing methods.
• No Duplicated Strings: Extracted warning messages and header keys into constants to avoid duplicated strings and ensure maintainability.

[stenalpjolly]

/gcbrun

[prernakakkar-google]

/gcbrun

[stenalpjolly]

/gcbrun

[anubhav756]

/gcbrun