Follow-up from !1: Check asserts and decide the naming to follow

PVE GUI and community.general proxmox modules have slightly different variables' naming, and the role's variable still have some diferencies with both. Modules doc is quite poor on some parameters, so let's clearly choose GUI naming and set appropriate links to doc.

Let's also check, test and eventually comlpete the asserts introduced in !1 (merged).

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The following discussion from !1 (merged) should be addressed: it was already addressed.

• @ulvida started a discussion:

  These assert tasks are very interesting to ensure parameters coherence (sometimes ansible errors for variables incoherence are not very clear). Thanks for the idea!

  In this case, to bring better info to user, shouldn't we put an information fail_msg, as you do in the next assert?