docs(maintenance): Add EoS check page

Author: Techassi

modules/concepts/pages/maintenance/eos.adoc

@@ -0,0 +1,25 @@
+= End-of-Support (EoS) check
+
+Since SDP 25.11.0 operators emit a warning message on startup and in a regular interval when it may have reached end-of-support.
+Most of our operators reach end-of-support one year after they have been released which roughly translates to three SDP releases.
+This is in accordance with our xref:compliance:policies.adoc[support policy].
+
+The interval can be adjusted or the check can be disabled completely via Helm values.
+
+[NOTE]
+====
+The following sections describe the available fields as well as their default and supported values.
+====
+
+[source,yaml]
+----
+maintenance:
+  endOfSupportCheck:
+    enabled: true # <1>
+    mode: offline # <2>
+    interval: 24h # <3>
+----
+
+<1> Boolean: `true`, `false`
+<2> Enum: `offline` (currently no other options available)
+<3> Duration: Any duration according to xref:reference:duration.adoc[this format]