[Doc] Update community contributors and versioning naming to follow vLLM (#5820)

### What this PR does / why we need it?

This pull request updates documentation to align with vLLM's community
standards.
- Change `Maintainers` to `Committers` to follow vLLM naming:
https://docs.vllm.ai/en/latest/governance/committers/
- Change release branch policy from `vX.Y.Z-dev` to `releases/vX.Y.Z`

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
doc ci passed
- vLLM version: v0.13.0
- vLLM main:
2f4e6548ef

Signed-off-by: Yikun Jiang <yikunkero@gmail.com>

docs/source/community/contributors.md

@@ -1,6 +1,6 @@
-# Maintainers and Contributors
+# Committers and Contributors
 
-## Maintainers
+## Committers
 
 | Name | Github ID | Date |
 |:-----------:|:-----:|:-----:|