Add icons for metoffice_warnings integration

[ianByrne]

Proposed change

Add link between existing metoffice logo and the new metoffice_warnings integration

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
• Replace an existing icon or logo with a higher quality version
• Replace an existing icon or logo after a branding change
• Removing an icon or logo

Additional information

• This PR fixes or closes issue: fixes #
• Link to code base pull request: Add Met Office Weather Warnings integration core#165602
• Link to documentation pull request: Add documentation for Met Office Weather Warnings integration home-assistant.io#44129
• Link to integration documentation on our website: Add documentation for Met Office Weather Warnings integration home-assistant.io#44129

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)