Implements Issue #1301 - Adds support for dumping current configuration
when SIGUSR1 signal is received by the kube-vip process.

Changes:
- Add SIGUSR1 signal handling in all manager start methods
- Implement configuration dump functionality in pkg/manager/manager_dump.go:
  * dumpConfiguration() - Main dump coordinator
  * 7 helper methods for different configuration sections
- Update signal handlers to use switch statement pattern
- Add comprehensive unit tests (5 tests, all passing)
- Add E2E test for signal handling

Implementation details:
- Thread-safe with mutex protection
- Non-disruptive: process continues after dump
- Output format: human-readable plaintext via stdout
- File organization follows project convention (manager_*.go pattern)

Co-authored-by: SteveYi <steveyiyo@steveyi.net>
Signed-off-by: thc1006 <84045975+thc1006@users.noreply.github.com>