Add capability to send messages to OSM users (notified via email)

[spwoodcock]

What type of PR is this? (check all applicable)

• 🍕 Feature
• 🐛 Bug Fix
• 📝 Documentation
• 🧑‍💻 Refactor
• ✅ Test
• 🤖 Build or CI
• ❓ Other (please specify)

Related Issue

Related to #1199
Related to #1573

Describe this PR

• I updated osm-login-python to return the raw OSM OAuth token too.
• This allows us to call the OSM API as needed, as the currently logged in user.
• Added a helper endpoint to send a test email to the currently logged in user.
• Last remaining things before ready:
  • Upgrade osm-login-python to v2.0.0 after merge of: Return the raw OSM OAuth2 token in addition to access_token osm-login-python#7
  • Upgrade osm-fieldwork --> v0.14.3 for latest fix to TMS URL as the same time.

Screenshots

I also received an email notification for the message 🎉

Alternative Approaches Considered

• Adding an SMTP service to the tech stack.
• Although managing both user email addresses and sending emails (without being marked as spam etc) is a hassle we don't need! (unless absolutely necessary).
• This approach makes our life a lot easier, as FMTM is OSM-centric (even for flows outside of OSM, we can project managers to just sign up to OSM, it's not a big deal).

Review Guide

• First login at: https://dev.fmtm.hotosm.org
• Then test the endpoint via API: https://api.dev.fmtm.hotosm.org

Checklist before requesting a review

• 📖 Read the FMTM Contributing Guide: https://github.com/hotosm/fmtm/blob/main/CONTRIBUTING.md
• 📖 Read the HOT Code of Conduct: https://docs.hotosm.org/code-of-conduct
• 👷‍♀️ Create small PRs. In most cases, this will be possible.
• ✅ Provide tests for your changes.
• 📝 Use descriptive commit messages.
• 📗 Update any related documentation and include any relevant screenshots.

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