Add complete attribute to .fleet-agents docs (elastic#127651) (elastic#129165)

* Add snapshot attribute to .fleet-agents docs

* Update docs/changelog/127651.yaml

* Fix changelog summary

---------

Co-authored-by: Eric Beahan <[email protected]>

Author: pkoutsovasilis

docs/changelog/127651.yaml

@@ -0,0 +1,5 @@
+pr: 127651
+summary: Add complete attribute to .fleet-agents docs
+area: Infra/Plugins
+type: bug
+issues: []

x-pack/plugin/core/template-resources/src/main/resources/fleet-agents.json

@@ -96,6 +96,9 @@
                     "snapshot": {
                       "type": "boolean"
                     },
+                    "complete": {
+                      "type": "boolean"
+                    },
                     "upgradeable": {
                       "type": "boolean"
                     },