[DOCS] Add deprecation docs for incompatible builds

[jrodewig]

We deprecated the es.unsafely_permit_handshake_from_incompatible_builds system
property in 7.11 with PR #65601. However, we didn't add a related item to the
7.11 deprecation docs. This adds the missing item.

Relates to #65753.

Preview

https://elasticsearch_77730.docs-preview.app.elstc.co/guide/en/elasticsearch/reference/7.x/migrating-7.11.html#deprecate-unsafely_permit_handshake_from_incompatible_builds

[jrodewig]

@elasticmachine test this please

[elasticmachine]

Pinging @elastic/es-docs (Team:Docs)

[elasticmachine]

Pinging @elastic/es-distributed (Team:Distributed)

[DaveCTurner]

LGTM2 although IMO it'd also be fine not to document this, we deliberately didn't document the setting in the first place, we just added it in case we had an emergency need to bypass those checks but we've never had such a need.

[jrodewig]

Thanks @DaveCTurner @masseyke!

IMO it'd also be fine not to document this, we deliberately didn't document the setting in the first place, we just added it in case we had an emergency need to bypass those checks but we've never had such a need.

I'll go ahead and merge/publish this since we have a corresponding breaking change in the 8.0 docs:
https://www.elastic.co/guide/en/elasticsearch/reference/master/migrating-8.0.html#breaking_80_transport_changes

Probably out of scope for this PR, but we should consider the criteria for not documenting a breaking change. We have quite a few for 8.0. It'd be great for users to have to parse through fewer of them.