Document Ubuntu ESM overlap period
Too many releases overlap in April - End of Standard Support for LTS release, End of ESM for LTS release, and a new interim release, plus often coincides for Easter.
Give slightly more time to start ESM. Whilst tokens and contracts are available ahead of time, continue to publish security updates through may into public security pocket, with ESM-only updates starting on 1st of June.
Whilst documenting such dates here is new, in practice this change is based on hindsight as all previous ESM support also continued to publish updates publically for some overlap time. Thus this is mostly documenting status quo.
18.04 LTS,Bionic Beaver,bionic,2017-10-19,2018-04-26,2023-[-04-26-]{+05-31+},2023-[-04-26-]{+05-31+},2028-04-26
20.04 LTS,Focal Fossa,focal,2019-10-17,2020-04-23,2025-[-04-23-]{+05-31+},2025-[-04-23-]{+05-31+},2030-04-23
22.04 LTS,Jammy Jellyfish,jammy,2021-10-14,2022-04-21,2027-[-04-21-]{+05-31+},2027-[-04-21-]{+05-31+},2032-04-21LP: #2003949
Edited by Dimitri Ledkov