[token-server] Accept uploaded token icons

Summary:
Provide all necessary handlers for migrating current token icon infra to token-server

• Support for image uploads at new endpoint
• Support in Cashtab for new server
• Telegram bot for mod approval/rejection

The telegram bot features are not tested in the app, though I have extensively tested them manually and locally. I looked into adding tests for this but the process is not straightforward (emulate telegram, emulate clicking on rendered telegram messages). Since this feature is used only by the admin, imo it is ok to leave automatic testing out. Expected that we will always have some degree of possible manual work with token icons.

While this diff is ready for review now -- some steps I will need to complete before landing

• Migrate existing token icons to token-server
• Update CI deploy step with telegram bot info
• Update token-server dir structure to support rejected icons
• Need D15746 to land to support automated icon rejections
• Land this one
• Shut down legacy token icon server

Test Plan: npm test

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D15744