[electroluxappliance] Readme.md corrections and JWT handling

[dag81]

This PR fixes typos in the README.md and implements JWT token handling improvements for the Electrolux appliance binding.

The changes correct documentation errors and add persistent storage for refresh tokens to improve authentication reliability.

• Corrects spelling errors in README.md including "serialNumber" typos and icon case standardization
• Adds JWT token storage functionality to persist refresh tokens across restarts
• Fixes incorrect category assignment for a "Powered On" channel from "Temperature" to "Switch"

(Thank you co-pilot for the summary :) )

[dag81]

Converting to draft as there will be more additions there appears to be issues with the JWT handling going on, when using the OpenJDK on our Linux server.

[dag81]

Soak testing now version 5 is on our server. I suspect the JWT refresh invalidates the old one. As my systems are file configured for easy restoration, when I updated the configs, I believe it reloaded the definitions including the original JWT. Therefore the additional changes add the JWT to be persisted so that if there is a double initialisation or a re-initialisation it is restored e.g. when file config's are done. I'll run this for a while and try a few file re-configs tomorrow, before marking the PR as non draft to make sure it continues running as it should, once I've confirmed no more JWT errors appear and loose comm's.

[dag81]

The changes work as expected when updating config files with the persisted token no more JWT errors happen, that require getting a new token.
The Category change was tested, the channels update with the new icon, and users can update their items if required, to the new definition.

[Copilot]

Pull Request Overview

This PR fixes typos in the README.md and implements JWT token handling improvements for the Electrolux appliance binding. The changes correct documentation errors and add persistent storage for refresh tokens to improve authentication reliability.

• Corrects spelling errors in README.md including "serialNumber" typos and icon case standardization
• Adds JWT token storage functionality to persist refresh tokens across restarts
• Fixes incorrect category assignment for a "Powered On" channel from "Temperature" to "Switch"

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
README.md	Fixes typos in parameter names and standardizes icon case formatting
thing-types.xml	Corrects category for "Powered On" channel from Temperature to Switch
ElectroluxApplianceHandlerFactory.java	Moves storage initialization to be shared across all handlers
ElectroluxApplianceBridgeHandler.java	Adds JWT token persistence using storage service