Ability to add placeholder to SearchBox from config

[MaxHershey]

Feature request

What problem does this feature solve?

Adds ability to add a placeholder to the search box component

What does the proposed API look like?

<SearchBox :placeholder="someStringHere" />
or

themeConfig: {
  search: {
     placeholder: someStringHere
  }
}

How should this be implemented in your opinion?

As a config object on the themeConfig

Are you willing to work on this yourself?

No