chore: bump node from 20 to 21

[abbiesims]

Done

• Bumps Node version from 20 to 21.
• Currently on Charmhub.io, we have some dependency conflicts when trying to upgrade packages as they require a higher version of Node.

How to QA

1. Run a project

• git clone https://github.com/canonical-web-and-design/charmhub.io/
• cd charmhub.io
• dotrun

2. Check the node version being used

• dotrun exec node -v
• In this case, it should output v20.16.0

3. Check-out this branch
4. Build this image docker build . --tag canonicalwebteam/dotrun-image:local
5. Run this image docker run -it -p 8045:8045 canonicalwebteam/dotrun-image:local /bin/bash
6. Build Charmhub.io again (dotrun build)
7. Node version should now be >= 21.0.0
8. Run Charmhub.io again (dotrun)

• Visit http://localhost:8045 and check that the website is running.

[samhotep]

LGTM!

Also Bumped the version to 1.2.0