Add upgrade motivation banner

[dieknolle3333]

Steps to test:

• mock an outdated WK version, e.g. by mocking getBuildInfo(), see comment in maintenance_banner.tsx
• see banner, make sure it looks good (e.g. across different themes)
• test link
• click it away
• it shouldn't be shown again, even if you log out / close the browser. it should only be shown again after another 3 days
• it should be shown again in a private browser tab though.

TODOs:

• fix styling of button, find out how to do theming well
• fix banner when browser window is narrow
• fix upcoming maintenance banner when user is logged out

Issues:

• fixes Add banner "Upgrade version" for self-hosted when version is older than 6 months #7745

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(Please delete unneeded items, merge only when none are left open)

• Updated changelog
• Removed dev-only changes like prints and application.conf edits
• Considered common edge cases

[dieknolle3333]

(obviously this can be set to true during testing, dont forget to remove)

[philippotto]

Cool stuff 😃 During testing, I noticed two things:

• I think the banner should only be shown when logged in. Showing this to external visitors doesn't make much sense, in my opinion.
• webknossos.org should be clickable probably (should open in a new tab)

[philippotto]

Testing went well mostly 🎉 However, when switching the theme while the banner is shown, the navbar height is not set properly:

If it's easy to fix, please go ahead. Otherwise, it's not that bad since the case is rather rare.

Also, see my two newest comments :)

[dieknolle3333]

@philippotto thanks for the feedback! actually it was quite easy to ensure the right nav bar height while switching the theme.

I also worked on the case that both a maintenance and an upgrade banner could be shown. I solved it so that only the maintenance banner is shown in that case. Once that is gone, the navbar height is broken (like in your last picture) though. I left it like that because the upgrade banner can be clicked away, because it is a rare case anyway and because fixing it would require letting maintenance and upgrade banner know about each other, which would need some refactoring. Let me know if you disagree and think that I should look into it further :)

[philippotto]

awesome :)