Bump flask from 0.12.5 to 1.0 in /backend/flask

Bumps [flask](https://github.com/pallets/flask) from 0.12.5 to 1.0.
- [Release notes](https://github.com/pallets/flask/releases)
- [Changelog](https://github.com/pallets/flask/blob/main/CHANGES.rst)
- [Commits](pallets/flask@0.12.5...1.0)

---
updated-dependencies:
- dependency-name: flask
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

backend/flask/requirements.txt

@@ -1,4 +1,4 @@
-Flask==0.12.5
+Flask==1.0
 Flask-Migrate==2.1.0
 Flask-SQLAlchemy==2.2
 Flask-Script==2.0.5