feat: Add support for Langfuse LLM Tracing via OTEL (#12905)

This PR adds LLM instrumentation on langfuse for ai-editor feature

## Type of change
New feature (non-breaking change which adds functionality)

Needs langfuse account and env vars to be set

## How Has This Been Tested?

I configured personal langfuse credentials and instrumented the app,
traces can be seen in langfuse.
each conversation is one session. 
<img width="1683" height="714" alt="image"
src="https://github.com/user-attachments/assets/3fcba1c9-63cf-44b9-a355-fd6608691559"
/>
<img width="1446" height="172" alt="image"
src="https://github.com/user-attachments/assets/dfa6e98f-4741-4e04-9a9e-078d1f01e97b"
/>


## Checklist:

- [x ] My code follows the style guidelines of this project
- [ x] I have performed a self-review of my code
- [ x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [ x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

---------

Co-authored-by: aakashb95 <aakash@chatwoot.com>
Co-authored-by: Vishnu Narayanan <iamwishnu@gmail.com>
Co-authored-by: Pranav <pranav@chatwoot.com>

.env.example

@@ -220,6 +220,7 @@ ANDROID_SHA256_CERT_FINGERPRINT=AC:73:8E:DE:EB:56:EA:CC:10:87:02:A7:65:37:7B:38:
 ## https://github.com/DataDog/dd-trace-rb/blob/master/docs/GettingStarted.md#environment-variables
 # DD_TRACE_AGENT_URL=
 
+
 # MaxMindDB API key to download GeoLite2 City database
 # IP_LOOKUP_API_KEY=