Add an introduction to `FLEET_SERVER_ELASTICSEARCH_CA_TRUSTED_FINGERP…

…RINT` (#409)

* Add an introduction to `FLEET_SERVER_ELASTICSEARCH_CA_TRUSTED_FINGERPRINT`

* Add include statement plus small edits

---------

Co-authored-by: David Kilfoyle <david.kilfoyle@elastic.co>

docs/en/ingest-management/elastic-agent/configuration/env/container-envs.asciidoc

@@ -115,6 +115,8 @@ include::shared-env.asciidoc[tag=fleet-server-cert-key-passphrase]
 
 include::shared-env.asciidoc[tag=fleet-server-insecure-http]
 
+include::shared-env.asciidoc[tag=fleet-server-es-ca-trusted-fingerprint]
+
 |===
 
 [discrete]

docs/en/ingest-management/elastic-agent/configuration/env/shared-env.asciidoc

@@ -287,6 +287,21 @@ Setting this to `true` is not recommended.
 
 // =============================================================================
 
+// tag::fleet-server-es-ca-trusted-fingerprint[]
+|
+[id="env-{type}-fleet-server-es-ca-trusted-fingerprint"]
+`FLEET_SERVER_ELASTICSEARCH_CA_TRUSTED_FINGERPRINT`
+
+| (string) The SHA-256 fingerprint (hash) of the certificate authority used to self-sign {es} certificates.
+This fingerprint is used to verify self-signed certificates presented by {fleet-server} and any inputs started
+by {agent} for communication. This flag is required when using self-signed certificates with {es}.
+
+*Default:* `""`
+
+// end::fleet-server-es-ca-trusted-fingerprint[]
+
+// =============================================================================
+
 // tag::fleet-enroll[]
 |
 [id="env-{type}-fleet-enroll"]