[STAR-2903] Add/Update documentation on how to configure/track sustainability targets

SprintCraft's new functionality from BB-6571, as well as adjustments to sustainability calculations from the same ticket, affect workflows around sustainability tracking at the cell and company level.

This PR updates relevant parts of the handbook to reflect the new workflows.

It also fixes some typos and removes private links.

Tickets

• STAR-2903

Related PRs

• opencraft/dev/sprintcraft!46 (merged)

Test instructions

• Read over diff and check out rendered changes here.

Reviewers

• @gabrieldamours