Investigate breaking changes between Rancher Dashboard and Extensions using Vue3

[cnotv]

Description

To avoid issues for all our customers upgrading Rancher, we must ensure that the upgrade process is not going to break their instances.

This includes cases where:

• Upgrade of Rancher to Vue3 while using Vue2 extensions
• Vue2 extensions are present in a Vue3 Rancher instance
• Vue2 Rancher version with Vue3 extensions

@nwmac Could we make it clear how we ensure avoiding issues for these cases?
Before the release, we will need to make these tests.

Context

While investigating how the Rancher dashboard is initialized, it seemed clear that there are possible issues with the way the same code is used by the extension due to the installation of plugins, directives, and so on.

This may be extended to any other breaking change between Vue2 and Vue3 syntax.

Implementation issue: #10660

[gaktive]

Can we collapse #10660 into this ticket? @nwmac & I are planning out 2.10.0 and these two sound like they should be done at the same time, otherwise this one sounds not as actionable as the prevention one.

[cnotv]

As I've written in the description of #10660:

Note: This is going to be part of the outcome for #11049

This means that someone has to plan how to deal with the extension and write it somewhere, so we are aware of it.
As last time I've been talking with @nwmac, there was a mechanism to be used in 2.9.0 with another breaking change which can be used as PoC.
If that is going to work, we can close accordingly issues:

• Prevent Extensions from breaking without providing info in case of Vue incompatibilities #10660, if nothing else is left to be done for Vue3 migration
• this issue if there's nothing to be known and it works out of the box, so as a confirmation that everything is going to be 100% fine

[aalves08]

I think this can be closed with the implementation of a proper gating mechanism as per #12071