Create LFX Mentoring administration guide

Create LFX Mentoring administration guide similar to [mentoring-wg/gsoc-org-admin-guide.md](https://github.com/cncf/mentoring/blob/main/mentoring-wg/gsoc-org-admin-guide.md) which would have:
* Admin responsibilities
* Program checklists & timelines
* Project idea proposal review guidelines
* New semester planning (what makes a good set of dates for an LFX term)
* etc.

Use mentoring-wg/gsoc-org-admin-guide.md as the reference and review the issue’s requested sections: responsibilities, checklists and timelines, project-idea review, and LFX term planning. Done means a comparable LFX Mentoring administration guide covers these workflows and any additional necessary guidance.

Written by the indexing model from the issue text.