fix(tui): Center the initially selected session in the session_list (resolves #8558)

[ariane-emory]

What does this PR do?

This PR attempts to ensure that the initially selected session when the session_list is opened is always within the viewport when opening the session list by trying to center it within the viewport.

Resolves #8558

Before (after following the procedure described in the issue)

After

How did you verify your code works?

A/B testing and running all tests in the project to ensure that no failures were introduced.