Update tasklist (#810)

* Save tasklist-24.svg, checkbox-24.svg

* add 16px

* Optimize SVGs

* Optimize SVGs

* Create beige-bats-switch.md

Co-authored-by: Ash Guillaume <actions@github.com>

Author: ashygee

.changeset/beige-bats-switch.md

@@ -0,0 +1,6 @@
+---
+"@primer/octicons": minor
+---
+
+- modifies tasklist icon proposed in https://github.com/github/primer/issues/746
+- adds a new checkbox icon using metaphor from previous tasklist metaphor