[open-period-notice] scheduled lambda function to send reminder emails

[sdunster]

... when a person forgets to sign out.

Summary: tbc

Test Plan: tbc

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• -> [open-period-notice] scheduled lambda function to send reminder emails #90
• [member self service period edit] button to send period edit email #84
• [member self service period edit] mutation to send period edit email #83

[sdunster]

Does this update the template (closed period vs open period) for emails triggered via button press as well?