Split the extension services from the IFE example

[ylussaud]

Split the extension services from the IFE example. This will allows to provide one plugin for the extension and several for the IFE example (one by Capella version).
Also add one optional feature for each version of the example

[ylussaud]

In practice it's a bit complicated to achive. We will stick with the current packaging.

[ylussaud]

It should be done to have a compatible range of M2Doc versions and of Capella versions