Add comprehensive Plex backup management scripts

- Introduced `restore-plex.sh` for restoring Plex backups with logging and validation.
- Created `test-plex-backup.sh` for automated testing of backup functionalities.
- Developed `validate-plex-backups.sh` for validating backup integrity and monitoring.
- Updated `update.sh` to reference the correct path for Plex service management.

plex/plex-management.md

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+# Plex Management Script Documentation
+
+This document provides an overview and step-by-step explanation of the `plex.sh` script. This script is used to manage the Plex Media Server service on a systemd-based Linux distribution.
+
+## Script Overview
+
+The script performs the following main tasks:
+
+1. Starts the Plex Media Server.
+2. Stops the Plex Media Server.
+3. Restarts the Plex Media Server.
+4. Displays the current status of the Plex Media Server.
+
+## Detailed Steps
+
+### 1. Start Plex Media Server
+
+```bash
+start_plex() {
+  sudo systemctl start plexmediaserver
+  echo "Plex Media Server started."
+}
+```
+
+This function starts the Plex Media Server using `systemctl`.
+
+### 2. Stop Plex Media Server
+
+```bash
+stop_plex() {
+  sudo systemctl stop plexmediaserver
+  echo "Plex Media Server stopped."
+}
+```
+
+This function stops the Plex Media Server using `systemctl`.
+
+### 3. Restart Plex Media Server
+
+```bash
+restart_plex() {
+  sudo systemctl restart plexmediaserver
+  echo "Plex Media Server restarted."
+}
+```
+
+This function restarts the Plex Media Server using `systemctl`.
+
+### 4. Display Plex Media Server Status
+
+```bash
+status_plex() {
+  sudo systemctl status plexmediaserver
+}
+```
+
+This function displays the current status of the Plex Media Server using `systemctl`.
+
+## Usage
+
+To use the script, run it with one of the following parameters:
+
+```shell
+./plex.sh {start|stop|restart|status}
+```
+
+- `start`: Starts the Plex Media Server.
+- `stop`: Stops the Plex Media Server.
+- `restart`: Restarts the Plex Media Server.
+- `status`: Displays the current status of the Plex Media Server.
+
+## Important Information
+
+- Ensure that the script is executable. You can make it executable with the following command:
+
+  ```shell
+  chmod +x plex.sh
+  ```
+
+- The script uses `systemctl` to manage the Plex Media Server service. Ensure that `systemctl` is available on your system.
+- The script requires `sudo` privileges to manage the Plex Media Server service. Ensure that you have the necessary permissions to run the script with `sudo`.
+
+By following this documentation, you should be able to understand and use the `plex.sh` script effectively.