[adoptium-pmc] Moving AdoptOpenJDK resources into Adoptium

[Tim Ellison <t.p.ellison@xxxxxxxxx>]

Hello all!

We are at the point where our projects are being created under the
Adoptium TLP, and we can start to plan the transition of AdoptOpenJDK
resources into those projects.

Obviously the transition is going to be a complex task.  We have many
moving parts, established processes, and enthusiastic contributors and
users to take care of throughout the transition.

Furthermore, we have a strict cadence of releases to maintain.  We don't
have the luxury of missing a quarterly release to sort out the
housekeeping, so we'll be "changing the engine while the car is driving
along the road".

With that in mind, and our next scheduled release being the last week of
April, I'm going to claim that we don't have time to move everything
from AdoptOpenJDK to Adoptium in time for that release.  Bear in mind
that moving resources includes getting through the EF processes too, so
timelines are not entirely within our control.

I propose that we transition resources piecemeal to the EF, and continue
to use them at AdoptOpenJDK to achieve our releases until we can make
the switch.

For example, we may start by moving the "openjdk-build" repo into the
Temurin location, submit an Eclipse CQ for clearances, start fixing
things up to require Eclipse committership to the repo, have
standardized source file headers in place, etc.  As that is happening we
‘hard switch’ AdoptOpenJDK to work from that repo exclusively, but still
build on our current infra, and publish into the AdoptOpenJDK repos and
website.  There will only ever be one "openjdk-build" repo.

That means we won’t build a parallel world in Eclipse and AdoptOpenJDK,
but rather smear the move and work more in EF and less in AdoptOpenJDK
as we go.  The repo migration plan [1] can be enhanced to specify a code
migration ordering.  Keep things working throughout.

I think 9 weeks to achieve a full transfer is … optimistic, so I expect
the April release binaries will likely only be hosted at
adoptopenjdk.net, having been built using EF code/resources that have
moved.  If we get further, great!

[1]
https://docs.google.com/spreadsheets/d/1r9zslP-pZw7-KXR1h-L_BJprvoaAaMqMvRkx5NnpVrI/edit?usp=sharing

Thoughts?
Tim