Having an RELEASE+1 I-Build repository early

[laeubi]

With the discussion here:

• https://github.com/eclipse-platform/eclipse.platform.releng.aggregator/discussions/863

and the first steps to automate most of the "opening" process e.g. here

• https://github.com/eclipse-platform/eclipse.platform.releng.aggregator/pull/883
• https://github.com/eclipse-platform/eclipse.platform.releng.aggregator/pull/876

I noticed that there is actual a little gap in the process regarding the I-Build repository, e.g. the buildscript currently references:

https://download.eclipse.org/eclipse/updates/4.27-I-builds/

but if we now want to open a new stream

https://download.eclipse.org/eclipse/updates/4.28-I-builds/

is not there (maybe created by the first I-Build with 4.28 stream?)

To ease the transition, and prevent multiple updates in the process of opening a stream, I'd like to suggest that there is always a

https://download.eclipse.org/eclipse/updates/(current release + 1)-I-builds/

repository, that simply points to the current release one unless a new item is published, that way automation workflows can easily update it (looking at the pom it might even using a variable).