vault: Add Eisenhower Matrix.md

[claremacrae]

Description

Show how to create an Eisenhower matrix using Tasks and Dataview.

Motivation and Context

See Discord

How has this been tested?

In the test vault, plus it's code I use all the time in my main vault.

Screenshots (if appropriate)

Types of changes

Changes visible to users:

• [x] Sample vault (prefix: vault - improvements to the Tasks-Demo sample vault)

Checklist

• [x] My code follows the code style of this project and passes yarn run lint.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] My change has adequate Unit Test coverage.

Terms

• [x] My contribution follow this project's contributing guide
• [x] I agree to follow this project's Code of Conduct