DOC-3505: Bump API version to 8.6.0 and correct 8.6 support end date

Set .api-version to 8.6.0 for the release and fix the 8.6 End of Premium
Support date to 2027-12-03 (18 months from the 2026-06-03 release date).

Author: kemister85

.api-version

@@ -1 +1 @@
-8.5.0
+8.6.0

modules/ROOT/partials/misc/supported-versions.adoc

@@ -6,7 +6,7 @@ Supported versions of {productname}:
 [cols="^,^,^",options="header"]
 |===
 |Version |Release Date |End of Premium Support
-|8.6 |2026-05-27 |2027-11-27
+|8.6 |2026-06-03 |2027-12-03
 |8.5 |2026-04-29 |2027-10-29
 |8.4 |2026-03-31 |2027-09-30
 |8.3 |2025-12-10 |2027-06-10