Add all CRUD methods

[karlhorky]

Currently, only the R in CRUD is showcased (Read using GET / SELECT)

Add Create, Update and Delete as well.

May make sense to connect this with creating blog_posts records with URLs, as described in:

• Add XSS example of insecure URL in database #28

‼️ End User Security: Come up with a security model for deploying this to Fly.io without allowing any user to attack other end users of the deployed website (eg. via XSS or other vectors)