Implement end to end tests and solve several bugs

[elchininet]

This pull request implements end-to-end tests to test the plugin directly in a Home Assistant instance using Playwright. During the building of the tests, several bugs were spotted and directly solved and covered:

• Fix js-template update using ‘states.entity’.
• Fix js-template update using states.domain when the domain contained an underscore
• Fix a bug about the js-template of the title not being updated if there were no items with js-templates.
• Fix a bug that provoked that some items were not matched in some ocassions.
• Fix a bug that were returning undefined as a string in templates with error or that return undefined.
• Fix a bug about the icon of an existing element not being updated because of an error.