Router factor out hotdeploy (#2466)

* refactor: delegate hot deployment logic to new `HotDeployer` interface and streamline related code in `Router`

* refactor: make `router` field in `DefaultHotDeployer` final for immutability

* fix: ensure proper cleanup and initialization of `hotDeployer` in `Router`

* refactor: enhance `Router` structure with streamlined initialization and reconfiguration logic

* refactor: improve thread synchronization in `DefaultHotDeployer` and add `getLock()` in `Router` for enhanced concurrency handling

* refactor: simplify `DefaultHotDeployer` by removing redundant `hotDeployingContexts` tracking and improve `Router` concurrency management

* refactor: replace `System.exit` calls with `StartupException` in `Router` and `RouterCLI` for cleaner error handling during startup

* refactor: remove redundant `errorNotice` logic and replace `System.exit` with `StartupException` in `RouterCLI` for cleaner error handling

* refactor: extract `tryToGetConfigurationFile` method in `RouterCLI` for cleaner and reusable configuration resolution logic

* refactor: improve error logging in `RouterCLI` and fix indentation for readability

* refactor: replace `StartupException` with `ExitException` for streamlined error handling and debugging in `Router` and `RouterCLI`

* refactor: relocate `ExitException` and rename method in `RouterCLI` for clarity and cohesion

* refactor: improve synchronization and streamline `DefaultHotDeployer` by replacing direct bean factory access with `Router.getRef`

* refactor: add synchronization to `DefaultHotDeployer.start` to prevent concurrent hot deployment initialization

* protect 'running' field by 'lock'

* added error, if Spring Context declares more than 1 router

* added comment

* refactor

* refactor: synchronize `DefaultHotDeployer.stop` and initialize `Router.hotDeployer` with `NullHotDeployer` to enhance thread safety and prevent NPEs

* refactor: simplify `Router.hotDeployer` initialization logic and clarify Javadoc for `setHotDeploy`

* refactor: streamline `Router.hotDeployer` initialization and enhance `HotDeployer` interface with `init` method

---------

Co-authored-by: Tobias Polley <mail@tobias-polley.de>

Author: predic8

core/src/main/java/com/predic8/membrane/core/ExitException.java

@@ -0,0 +1,13 @@
+package com.predic8.membrane.core;
+
+/**
+ * Exception that signals that the startup failed and that Membrane should exit.
+ * It doesn't have a context or message cause it just signals that the program should exit.
+ * By using the exception, it is possible to exit at only one place. That makes debugging and testing
+ * of the Router class easier.
+ * The exception is in this package instead of the cli package not to introduce a dependency to cli.
+ *
+ * TODO: Move exception to router subpackage together with Router.
+ */
+public class ExitException extends RuntimeException {
+}