eol notice: escalate to warning only shortly before EOL

eol notice: escalate to warning only shortly before EOL

The EOL message is positioned quite noticeable already in all our
products, being always visible. So use a notice-style for the icon
and its color until three weeks before EOL, when we switch to a
critical warning.

As it can be OK to run a, e.g., PVE 7 setup shortly before its EOL,
if, for example, one plans to replace it completely and decommission
the old one (so upgrade before EOL would be just extra work).

Using three weeks for the cut-off has no in-depth, heavily thought
out Good Reason™, but was rather chosen as it's likely to be noticed
before the actual EOL in somewhat actively maintained setups (e.g.,
admin checking in every week or two) and can give admins further
means to escalate things with higher ups. Also weeks are always 7
days, while months aren't uniform, so the former is easier to
communicate.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>