Compatibility check in add-node

[DavidePrincipi]

If a worker node is created from an old prebuilt image and joins an existing cluster, we must check whether its core version is compatible with the leader's core version.

For example, if the Redis releases are incompatible, the SYNC replica will fail, leading to a complex recovery scenario.

Checking the worker node version during the add-node action ensures that incompatible core versions do not join the same cluster, preventing unexpected errors.

Discussion https://mattermost.nethesis.it/nethesis/pl/8ww1sxu5cibopbezo388wmsu8o

See also NethServer/ns8-core#830 (review)

[DavidePrincipi]

In testing

• Core 3.7.0-dev.1
• Docs feat(add-node): avoid core version mismatch ns8-docs#159

Test case 1

Join Leader Core 3.6 with Worker 3.7. The join is (still) allowed.

Test case 2

Join Leader Core 3.7 with Worker 3.7. Join allowed.

Test case 3

Join Leader Core 3.7 with Worker 3.6. Join forbidden. An error message is displayed in the UI.

Test case 4

• Join Leader Core 3.7 with NS7 nethserver-ns8-migration-1.2.1. Join not allowed.
• Join Leader Core 3.7 with NS7 nethserver-ns8-migration-1.2.1-1.1.gdffa2ac.ns7.x86_64.rpm nethserver-ns8-migration-1.2.1-1.2.gf2ba28d.ns7.x86_64.rpm from testing. Join allowed.