Improve prioritization of LZ checklist

[erjosito]

Existing LZ checklist has most of the items classified as "Medium". We should probably objectively decide what the three different levels mean, and reclassify the checks.

For example, as description of the levels something like:

• High: mandatory recommendation, regardless of customer requirements
• Medium: this recommendation can have a large impact in the design, but it is not necessarily mandatory
• Low: nice to have

After the meaning of the priorities is decided, we should reprioritize the different checks of the LZ checklist.

[brsteph]

• The current list does have High, Medium, and Low, but we can still use this item to align. It might make sense to combine this with other review items.

[brsteph]

As part of #792, some of the priorities are adjusted.