[lecture] An intro lecture on finite horizon cake-eating problem

[shlff]

Proposed by @jstac we can add a lecture on finite horizon cake-eating problem in intro lecture series.

Reference:

• https://python.quantecon.org/cake_eating_problem.html
• https://python.quantecon.org/cake_eating_numerical.html
• https://jax.quantecon.org/cake_eating_numerical.html