dashboard: Add Streamlit dashboard for benchmark result visualization

Adds a new Streamlit-based dashboard for visualizing benchmark data
from the resultstore. The dashboard script enables interactive views
of kernel performance results filtered by SUT, config, and benchmark.
It uses Altair charts for statistical plots and includes data tables.
The __init__.py file is added to support dashboard module structure.

Signed-off-by: Aishwarya TCV <aishwarya.tcv@arm.com>