Move to messages instead of message parts

[ecayer]

Previously, Notify accounted its quotas in terms of message parts, but going forwards, the agreements deal only in messages, not message parts. Specifically, MOU partners used to get 250k message parts free, but the latest agreements give them 100k messages instead.

We need to

• remove references to message parts throughout the product
• ensure that quotas and graphs are expressed in messages, not message parts, in the UI
• ensure any send cutoffs are handled correctly
• maintain records of both messages and message parts going forwards (so that we can review our pricing assumption that a message is typically about 2.5 parts).
• prepare messaging to partners to explain this change

Ideally, we'll also have some way to grant messages beyond the 100k quota to match the agreement with the one partner who is put over their previously-signed quota limit by this change.

[dmvancura]

so tasks to take on:
review site content to find all reference to message parts
note reference of 'message parts' within one ticket to change all references to messages
will continue this

[ccostino]

@ecayer and @dmvancura, we have another epic with more details and information here - GSA/notifications-api#1427 - let's consolidate these into one if we can! 🙂

[ecayer]

Doh! Moving any additional notes over there and closing this one. Thank you, Carlo!