Docs: Autofocusing on search field in search dialog

[LuisThe0ne]

Description

When clicking on the search icon in the upper right corner of the documentation start page, the input field in the opening dialog is now autofocused. The field not being autofocused is sometimes annoying when you already start typing a search query, but you forgot to click on the input field. Solves #8012

How Has This Been Tested?

I built the Docs.Server project opened the dialog and the field was autofocused

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

MudBlazor.Search.field.autofocus.mp4

Checklist:

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[mikes-gh]

Thanks @LuisThe0ne 👍