Refactor JWT-generation methods out of ReportingAPI controller and into the model

[aldavidson]

An 'under the hood' PR which does two things:

1. Moves the JWT-generation methods out of the OneTimeTokens controller, and into the OneTimeToken model.

This is tidier, and also enables a one-liner in the console which is useful when developing locally:

> jwt = ReportingAPI::OneTimeToken.find_or_generate_for!(user: User.first, cis2_info: {...}).to_jwt

2. Adds a JWT_SIGNING_ALGORITHM constant to define the HS512 algorithm in one place, rather than hard-coding it everywhere

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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