New REST-like admin API

[matrixbot]

This issue was originally created by @sandhose at matrix-org/matrix-authentication-service#3057.

MAS provides a new REST-like admin API

• Bootstrap a new REST-like admin API matrix-org/matrix-authentication-service#2993
• Host a Swagger UI both in the static documentation and by the server matrix-org/matrix-authentication-service#3018
• Add admin API to create users matrix-org/matrix-authentication-service#3019
• Set password admin API matrix-org/matrix-authentication-service#3021
• Lock user admin API matrix-org/matrix-authentication-service#3022
• Unlock user admin API matrix-org/matrix-authentication-service#3023
• Deactivate user admin API matrix-org/matrix-authentication-service#3030
• Document the admin API matrix-org/matrix-authentication-service#3038
• OAuth 2.0 sessions list and get admin APIs matrix-org/matrix-authentication-service#3031
• Admin API to list and get user emails #4001
• Admin API to list and get compatibility sessions #4002
• Admin API to list and get user sessions #4004
• Admin API to add and delete user email addresses #4039

[turt2live]

I've made a (terrible) attempt at the start of email listing here: #3992

[sandhose]

Closing this in favour of individual sub-issues