Langfuse integration breaking - new release neeeded

[TuanaCelik]

Describe the bug
The community have reported on discord that they're encountering errors due to the deprecated ChatMessage.to_openai_format() function which seems to have been fixed in this commit but it may be worth testing this.

Here's the original PR for it

They are currently resolving it by pip installing this branch. :
pip install -U git+https://github.com/deepset-ai/haystack-core-integrations.git@main#subdirectory=integrations/langfuse

Looks like we may have to make a new release for the fix to be available in the package.

PS: For more context, refer to this Discord thread and the users Jibran and LastRemote:

[vblagoje]

Fixed with new langfuse-haystack release. The fix was in place already but we forgot to cut a new release. Suggest closing @TuanaCelik