Update portainer to version 2.21.0

[nmfretz]

🤖 This is an automated pull request to update portainer to version 2.21.0. This PR must be reviewed and tested before merging.

[github-actions[bot]]

🎉   Linting finished with no errors or warnings   🎉

Thank you for your submission! This is an automated linter that checks for common issues in pull requests to the Umbrel App Store.

Please review the linting results below and make any necessary changes to your submission.

Linting Results

Severity	File	Description
ℹ️	portainer/docker-compose.yml	Mounted file/directory "/portainer/data/docker" doesn't exist: The volume "${APP_DATA_DIR}/data/docker:/data" tries to mount the file/directory "/portainer/data/docker", but it is not present. This can lead to permission errors!
ℹ️	portainer/docker-compose.yml	Mounted file/directory "/portainer/data/portainer" doesn't exist: The volume "${APP_DATA_DIR}/data/portainer:/data" tries to mount the file/directory "/portainer/data/portainer", but it is not present. This can lead to permission errors!
ℹ️	portainer/docker-compose.yml	Mounted file/directory "/portainer/data/docker" doesn't exist: The volume "${APP_DATA_DIR}/data/docker:/var/run" tries to mount the file/directory "/portainer/data/docker", but it is not present. This can lead to permission errors!
ℹ️	portainer/docker-compose.yml	Potentially using unsafe user in service "docker": The default container user "root" can lead to security vulnerabilities. If you are using the root user, please try to specify a different user (e.g. "1000:1000") in the compose file or try to set the UID/PUID and GID/PGID environment variables to 1000.
ℹ️	portainer/docker-compose.yml	Potentially using unsafe user in service "portainer": The default container user "root" can lead to security vulnerabilities. If you are using the root user, please try to specify a different user (e.g. "1000:1000") in the compose file or try to set the UID/PUID and GID/PGID environment variables to 1000.
ℹ️	portainer/docker-compose.yml	Service "docker" uses host network mode: The host network mode can lead to security vulnerabilities. If possible please use the default bridge network mode and expose the necessary ports.

Legend

Symbol	Description
❌	Error: This must be resolved before this PR can be merged.
⚠️	Warning: This is highly encouraged to be resolved, but is not strictly mandatory.
ℹ️	Info: This is just for your information.

[nmfretz]

🤖 This is an automated summary of installation tests:

• ✅ App installs successfully in umbrel-dev VM

• ✅ App UI returns a 200 status code

• 📸 UI screenshot:

This PR must still be reviewed and tested before merging.

[nmfretz]

Bumped dind to latest.

Reviewed and tested.