Proposed change

Since the change home-assistant/frontend#4581, the entity is not required anymore for the Lovelace button, but documentation still says it does: https://www.home-assistant.io/lovelace/button/#entity

This updated the documentation by replacing the "(Required)" label with "(Optional)" and also updates the sample to show this change.

Type of change

• Spelling, grammar or other readability improvements (current branch).
• Adjusted missing or incorrect information in the current documentation (current branch).
• Added documentation for a new integration I'm adding to Home Assistant (next branch).
• Added documentation for a new feature I'm adding to Home Assistant (next branch).
• Removed stale or deprecated documentation.

Additional information

• Link to parent pull request in the codebase: (not applied)
• This PR fixes or closes issue: Lovelace button docs should not have "entity" as required #12452

Checklist

• This PR uses the correct branch, based on one of the following:
  • I made a change to the existing documentation and used the current branch.
  • I made a change that is related to an upcoming version of Home Assistant and used the next branch.
• The documentation follows the Home Assistant documentation standards.