During import, only trigger "update project configuration" on Maven projects if necessary

[fbricon]

When workspace is reopened, we always update Maven project configurations, which is CPU and Memory inefficient (see eclipse-che/che#8335 (comment)).

We basically need to implement : https://github.com/eclipse/eclipse.jdt.ls/blob/f08b7c215d7e03597f5f0a91ac91380c90c9787e/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/managers/MavenProjectImporter.java#L189-L192

I think, one way to do it it to check if the project pom.xml is more recent than the last workspace serialized state file.