issue: #38399
- add metrics for broadcaster component.
- add metrics for wal flusher component.
- add metrics for wal interceptors.
- add slow log for wal.
- add more label for some wal metrics. (local or remote/catcup or
tailing...)
Signed-off-by: chyezh <chyezh@outlook.com>
issue: #38399
- Make a timetick-commit-based write ahead buffer at write side.
- Add a switchable scanner at read side to transfer the state between
catchup and tailing read
Signed-off-by: chyezh <chyezh@outlook.com>