Upgrade guest to member

@DSASanFrancisco/portal-members

Summary

• Added an API endpoint that upgrades the given member_id to a full member
• Attempts to create the member role, invite the member to auth0, and send out the welcome email
• Returns a response of all the actions taken

Remaining Work

• Add unit tests
• Fix all existing unit tests

I have:

• Included a summary of the changes
• Linked to this merge request from AirTable
• Add all dependent merge requests