Document SESSION_STORE_ARGS as optional in starter project settings

[ravi-kumar-pilla]

Motivation and Context

Resolves https://github.com/kedro-org/kedro-viz/issues/1951

This is a documentation update for the PR - https://github.com/kedro-org/kedro-viz/pull/1915

NOTE: Kedro-Viz had a bug in handling the parent directory creation for default session_store path. The tests in this PR are failing due to the same issue. We should merge this PR after the new release of Kedro-Viz which has the bug fix.

ValueError: 
(sqlite3.OperationalError) unable to open database file
(Background on this error at: https://sqlalche.me/e/20/e3q8).
Failed to instantiate session store of type 
'kedro_viz.integrations.kedro.sqlite_store.SQLiteStore'.

How has this been tested?

• Documentation for user reference in the starters

Checklist

• [x] Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• [x] Assigned myself to the PR
• [ ] Added tests to cover my changes