check for new CARTA release

[kswang1029]

This is considered as a good way to notify existing users that there is a new CARTA release. Mostly useful for UDM I guess.

• the frontend checks regularly (daily?) if there is a new CARTA release. Maybe there is a way by checking Github using curl? If there is a new version available, show a popup and guide users where to get it.
• in the Help manual, add an option as "Check for update" so users can trigger the check manually anytime too.

[kswang1029]

doing
curl -H "Accept: application/vnd.github.v3+json" https://api.github.com/repos/CARTAvis/carta/releases
can retrieve all releases info in json format.

The first one is the latest one with "tag_name": "v3.0.0-beta.3" so I guess we can compare the frontend tag and if they are not identical, there is a new release on GitHub. Not sure if it is that simple? @veggiesaurus @YuHsuan-Hwang