Make Task Operations Great Again (aka more secure)

[vincanger]

Description

Fixes #401 by updating and deleting task where userId === context.user.id

Contributor Checklist

Make sure to do the following steps if they are applicable to your PR:

• [] Update e2e tests: If you changed the /template/app, then make sure to do any neccessary updates to /template/e2e-tests also.
• Update demo app: If you changed the /template/app, then make sure to do any neccessary updates to /opensaas-sh/app_diff also. Check /opensaas-sh/README.md for details.
• Update docs: If needed, update the /opensaas-sh/blog/src/content/docs.

[sodic]

LGTM.
@vincanger if you tested it and it works, feel free to merge when ready :)