feat: custom payload admin components

[vincenttao04]

🆔 Jira Ticket Number

AUSCO-105

📝 Description

• Created 3 new custom components, rendered on the payload admin site (welcomepanel, legacypanel, endpanel)
• The 3 custom components hold details that are useful to future non-technical users of ausco/payload.
• Created 1 new layout component which hosts the welcome and endpanel, as these render on top of the dashboard.
• endpanel renders at the bottom of the dashboard.

✅ Checklist

• All Next.js build checks are passing.
• I have performed a self-review of my code.
• I have commented my code in hard-to-understand areas.
• I have moved my Jira ticket from IN PROGRESS to READY TO REVIEW.
• I have verified that my pull request is merging my branch (right side) into the main branch (left side) - see the top banner, underneath the "Open a pull request" header.

📸 Notes

🚨 Risks

cannot seem to fix type error when importing custom components into payload.config.ts. only way around it was to set the custom components as type any:
on lines 42 to 45:
components: { beforeDashboard: [StartLayout] as any, afterDashboard: [EndPanel] as any, },