Release 1.6.0 update branch

Step of the release process detailed in: #614 (closed)

TL;DR

This perform the release for VTK-m 1.6.0. This will bring to release everything up to d2d1c854 the commit plus other things such as release notes .

Change on the releasing branch scheme

This release will introduce a different release method described at !2450 (merged)

The main different to how it was before is that:

• This update branch is branched of from the latest release (or tip of release branch)
• This update branch brings the changes of master by doing a git merge -X theirs master in the first commit of the update branch.