Fix outlook render bug in newsletters

This MR tries to fix render issues with old IE and Outlook versions that have been reported several times (ugh)

• add explicit px-based width for graphs
• replace svg by png
• Doing this for the Newsletter Oct 2022 and Dec 2022.
• June 2022 NL was formatted in the old version anyway
• Future newsletter (April 2023) will need corresponding adaptation !691 (merged)

assigned to @jandt-desy

changed the description

changed title from Fix outlook render bug in nextletters to Fix outlook render bug in newsletters

merged

mentioned in commit 2443c0fb

mentioned in merge request !691 (merged)