feat: expand MessageIntent support for message creation

[esther-tock]

Fixes

Fixes #950
This pull request adds support for MessageIntent in message creation and expands the Message.MessageIntent enum to include the newly supported intent values (for example otp, customercare, etc.). It ensures the Java helper can serialize MessageIntent correctly on Messages create requests while preserving compatibility with existing intent values like otp, notifications, fraud, and marketing.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

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[sbansla]

@esther-tock These APIs are autogenerated from open api specs. Once this feature is made public it will be available via sdk.
For your testing purpose for feature which are not yet GA, SDK jar is provided through different channel. Can you contact your product manager who can connect with Twilio.