[Feature request] add getScopePageTitle function for frontmatters' option

[GNQG]

Feature request

What problem does this feature solve?

The title of a scope page for some frontmatter's key (ex. /tag/sometag/) is able to be set like getPaginationPageTitle. Currently it is automatically set to "${key} ${entryTitle}" here.

What does the proposed API look like?

Almost same as getPaginationPageTitle. Add getScopePageTitle: (key: string) => string to frontmatter option.

If like bellow, the title will be set to "tag=foo | ${project_title}" with default theme:

{
  // ...,
  frontmatters: [
    {
      // ...,
      scopeLayout: 'SomeScopeLayout',
      getScopePageTitle(key) {
        return `tag=${key}`;
      }
    },
    // ...,
  ]
}

How should this be implemented in your opinion?

Are you willing to work on this yourself?

Yes I have already implemented this locally.