Add release-notes gitlab CI template

Loic Nicollerequested to merge
add_release_template into main

What does this MR do and why?

Add the release-notes gitlab ci template to sylva-core. The release notes could be customized with the use of :

.release-notes-before-script:
  - []

.release-notes-after-script:
  - []

if needed, and can as always be edited manually to add specific infos

Edited by Thomas Morin

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