Introduce a ScannerStartupDelay configuration to enable WAL write-only
recovery, allowing fence messages to be persisted during
primary–secondary switchover when the StreamingNode is trapped in crash
loops.
issue: https://github.com/milvus-io/milvus/issues/46368
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit
* **New Features**
* Added a configurable WAL scanner pause/resume and a consumer request
flag to optionally ignore pause signals.
* **Metrics**
* Added a scanner pause gauge and pause-duration tracking for WAL
scanning.
* **Tests**
* Added coverage for pause-consumption behavior and cleanup in stream
client tests.
* **Chores**
* Consolidated flush-all logging into a single field and added a helper
for bulk message conversion.
<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->
---------
Signed-off-by: bigsheeper <yihao.dai@zilliz.com>
issue: #38399
We want to support broadcast operation for both streaming and msgstream.
But msgstream can be only sent message from rootcoord and proxy.
So this pr move the streamingcoord to rootcoord to make easier
implementation.
---------
Signed-off-by: chyezh <chyezh@outlook.com>
