Raise minimum requirements to Java 11 and AEM 6.5

[kwin]

Given that soon AEMaaCS will support Java 21 and AEM 6.5 will support Java 17 it is time to leverage new Java features also in ACTool and drop support of Java 8 and AEM 6.4. That allows to get rid of some more third party dependencies like Apache Commons IO (usually Java API provides reasonable alternatives) or Apache HTTP Client (to be replaced by Java HTTP Client) and in general leverage new Java API/features.

[ghenzler]

I think there are still some customers that run AEM 6.5 on Java 8 (probably more than we think)... but they can keep using the current version until they upgrade Java (let's use a minor version bump though so worst case we could provide a fix for java 8 and 3.4.x if needed, even if it's unlikely)

[kwin]

I would indicate with a major version bump that requirements changed, i.e. 4.0.0