Bug: WebApp version isn't always updated on server upgrades

[chenilim]

Steps to reproduce the behavior:

1. Install Focalboard plugin v0.7.0
2. Open the Focalboard workspace
3. Note the displayed version (should be 0.7.0)
4. Remove the plugin from the server
5. Install Focalboard plugin v0.7.3 (or another different version), via custom plugins on the server
6. Close and reopen the Focalboard workspace
7. Note the version number - in some cases this is still 0.7.0

A force-reload of the browser will update the webapp to the latest version

Expected behavior:
The webapp always shows the currently installed version.

Platform:

• Chrome 91 on macOS 11.4

Additional context:
It appears that the browser caches the old version of the webapp. We may need code changes to force it to load the latest version, e.g. by appending a guid / timestamp to the webapp file names.

[chenilim]

@sbishel, I think this one is worth investigating and fixing earlier, before we get many more upgrade scenarios out there. Please reassign as needed. Thanks.