add lawn mower icon

[mikey0000]

Proposed change

As per architecture discussion here home-assistant/architecture#894
adding icon for the lawn_mower entity

Type of change

• Add a new logo or icon for a new core integration
• Add a missing icon or logo for an existing core integration
• Add a new logo or icon for a custom integration (custom component)
  • I've opened up a PR for my custom integration on the Home Assistant
    Python wheels repository
• Replace an existing icon or logo with a higher quality version
• Removing an icon or logo

Additional information

Link to core integration pull request: home-assistant/core#93623
Link to documentation pull request: home-assistant/home-assistant.io#28546
Link to frontend pull request: home-assistant/frontend#17558
Link to developer documentation pull request: home-assistant/home-assistant.io#28546

Checklist

• The added/replaced image(s) are PNG
• Icon image size is 256x256px (icon.png)
• hDPI icon image size is 512x512px for (icon@2x.png)
• Logo image size has min 128px, but max 256px, on the shortest side (logo.png)
• hDPI logo image size has min 256px, but max 512px, on the shortest side (logo@2x.png)

[frenck]

✅ Approved. Can be merged as soon as the parent PR gets merged.