feat: home slot for customizing the entire homepage easily

[soulsam480]

This PR adds a slot for the entire home page for easy customization

Reason

• Currently when someone wants to just modify the homepage with custom style, it's not possible to extend.
• The current homepage slots i.e. home-hero. home-features, home-footer only allow customizing specific parts.

How this addition helps

Currently

<script setup lang="ts">
import Layout from 'vitepress/dist/client/theme-default/Layout.vue';
</script>

<template>
  <Layout>
    <template #home-hero>
      <p>My custom hero data</p>
    </template>
    <template #home-features>
      <p>My custom feature data</p>
    </template>
    <template #home-footer>
      <p>My custom footer data</p>
    </template>
  </Layout>
</template>

In this pr

<script setup lang="ts">
import Home from './components/Home.vue';
import Layout from 'vitepress/dist/client/theme-default/Layout.vue';
</script>

<template>
  <Layout>
    <template #home>
      <Home />
    </template>
  </Layout>
</template>

This will add more flexibility to vitepress while customizing the default Homepage