[FEATURE] Observability Homepage dashboard

[YANG-DB]

Is your feature request related to a problem?
Currently the landing page for Observability has no real reflection of the content or capabilities of the Observability plugin

What solution would you like?

1. Add an Observability Homepage dashboard that can be used for playground or as the default OSS deployment dashboard explaining all the features and capabilities

• adding reference to the Observability Playground

2. Adding a link from the default playground to the Observability playground

What alternatives have you considered?
N/A

Do you have any additional context?

• https://playground.opensearch.org/app/home#/
• https://observability.playground.opensearch.org/app/home#/