Reduce chance of piling up notifications after a reload

[fregante]

What does this PR do?

• Fixes this specific comment Cleanup widgets and side effects on context invalidated (reload, update) #4258 (comment)

In short:

• changes the duration from "infinity" to "20s"
• cleans up some naming to follow existing best-practices (e.g. what unit is duration?)

Discussion

In that issue I mentioned we should remove the elements from previous installations, but in the case of the notifier, this is impossible:

• the notification specifically appears after the invalidation, so we can't also remove it
• technically the content scripts will be "active" until the next page reload, and they could still trigger notifications. I don’t think it's 100% safe to remove them entirely

So for this reason I think it makes sense to shorten to duration of the final notification, so eventually it will be automatically dismissed.

Checklist

• Designate a primary reviewer: anyone

[fregante]

• webpackMode: "lazy" is the default
• webpackChunkName was only disabled because the previous webpackMode did not create a chunk

[github-actions]

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