Add benefits/impact questions to TI funding request template

[marcelamelara]

From our Q2 2024 TI funding request reviews, common questions asked to submitted requests revolved around why the requested effort is beneficial to the project/broader OpenSSF ecosystem, and what the impact of not funding is. These questions should become part of the default template as they provide important motivation and context, and help the TAC in prioritizing requests.

Inspired by @SecurityCRob in https://github.com/ossf/tac/issues/328#issuecomment-2117534054