Add an availability heatmap section to group triage reports

• Adds an availability heatmap section to the group triage report template

The heatmap will show S/P labels for open availability issues for the group

Generated examples for ~"group::access" triage report

Example screenshot

Example markdown

Availability Section

Heatmap for all availability issues

Availability issues for their priority and severity label are counted here. Every availability issues should have severity and priority labels applied. Please take a look at the issues which fall into the columns indicating that the priority or severity labels are currently missing.

	severity1	severity2	severity3	severity4	No severity
priority1	0	0	0	0	0
priority2	0	0	1	0	0
priority3	0	0	0	0	0
priority4	0	0	0	0	0
No priority	0	0	0	1	1

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Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Week-in-review

Closes #406 (closed)