Add end of Legacy Support dates (new eol-legacy column)
The optional Legacy support add-on on top of Ubuntu Pro extends the security maintenance and support for an additional 2 years, resulting in 12 years coverage overall. That information is already publicly present in the Release Cycle page [1].
Add a new eol-legacy column for the legacy support and add the dates
for the supported LTS version. The Release Cycle page [1] mentions only
the month. So just add two years to the ESM end of life dates and pick
the next day that falls in the Tuesday to Thursday range.