Support of Cache-Control header is only partial

[NiccoMlt]

While looking at the block code below to figure out if WebP images would be cached correctly:

https://github.com/diennea/carapaceproxy/blob/fe1cfdfec3c52a8f004ad9676a3e3a386f71a131/carapace-server/src/main/java/org/carapaceproxy/server/cache/ContentsCache.java#L188-L200

we figured out that caching strategy implemented by isChached methods is a little naïve. Taking a look the the actual code:

https://github.com/diennea/carapaceproxy/blob/fe1cfdfec3c52a8f004ad9676a3e3a386f71a131/carapace-server/src/main/java/org/carapaceproxy/server/cache/ContentsCache.java#L122-L131

https://github.com/diennea/carapaceproxy/blob/fe1cfdfec3c52a8f004ad9676a3e3a386f71a131/carapace-server/src/main/java/org/carapaceproxy/server/cache/ContentsCache.java#L155-L172

it is especially evident that we don't actually support all the Cache-Control values.

Request	Response
max-age	max-age
max-stale	-
min-fresh	-
-	s-maxage
no-cache	no-cache
no-store	no-store
no-transform	no-transform
only-if-cached	-
-	must-revalidate
-	proxy-revalidate
-	must-understand
-	private
-	public
-	immutable
-	stale-while-revalidate
stale-if-error	stale-if-error