Update handbook with correct labels/workflow

Why is this change being made?

As per a recent slack conversation, we are moving to Package::p1/2 labels to better prioritize and schedule work. This change, removes the package::triage column, as we will now use the P1/2 labels.

I also updated the Package:scheduling board to include:

• workflow::scheduling
• Package::p2
• Package::p1

Does this MR meet the acceptance criteria?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what