Propage request id to chat service

Send request id to chat service in headers.
<think>
PR Context:
- Title: fix(chat): append request id to headers for chat request
- Merged: 2025-07-25T07:27:38Z
- Files changed: 4 files
- Commits: 7 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [x] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates
- [ ] Documentation
- [ ] CI/CD

## Description
Propagation request-id to chat service for consistency.
Propagate chat session id as well in request
Add count metric for chat api


### Additional Changes

- [ ] This PR modifies the API contract
- [ ] This PR modifies the database schema
- [ ] This PR modifies application c
</think>

To implement this, you'll need to modify:


**Detailed Implementation:**


**Commit 1:** fix(chat): append request id to headers for chat request (#8680)
Files to modify:


**crates/common_utils/src/consts.rs**
  Modify existing code

**crates/router/src/core/chat.rs**
  Modify existing code

**crates/router/src/routes/chat.rs**
  Modify existing code

**crates/router/src/routes/metrics.rs**
  Modify existing code
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