Improvements to registration and authorization

[bob2021]

• Using a Number type for the invoice amount when registering via invoice throws an error for amounts like 234.00 because the trailing zeros are stripped off, so a string must be used instead.
• Auth token is now fetched/checked just before the request is made, to help avoid using an expired token.
• The connector's base url is now overridden for authentication requests, so a connector using a different base url can still authenticate.
• Added missing 429 responses
• Added support for locking during authentication
• Added rate limiting for authentication to avoid a 10min lockout if the threshold is exceeded (15 req/5s)
• Switched php-compatibility version to dev-develop to fix false positive using $this in an enum (there are no recent tagged versions, and apparently none coming for the foreseeable future)
• Added header parameters missing from generated registration API.

[colinmollenhour]

Awesome work!