elasticsearch-keystore: add page (#17123)

Co-authored-by: Machiavelli <145562237+MachiavelliII@users.noreply.github.com>
Co-authored-by: Wiktor Perskawiec <wiktor@perskawiec.cc>

pages/common/elasticsearch-keystore.md

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+# elasticsearch-keystore
+
+> Manage secure settings (e.g., passwords, tokens, and credentials) used by Elasticsearch.
+> More information: <https://www.elastic.co/guide/en/elasticsearch/reference/current/elasticsearch-keystore.html>.
+
+- Create a new keystore (not password-protected):
+
+`elasticsearch-keystore create`
+
+- Create a new password-protected keystore:
+
+`elasticsearch-keystore create -p`
+
+- Add a setting interactively:
+
+`elasticsearch-keystore add {{setting_name}}`
+
+- Add a setting from standard input:
+
+`echo "{{setting_value}}" | elasticsearch-keystore add --stdin {{setting_name}}`
+
+- Remove a setting from the keystore:
+
+`elasticsearch-keystore remove {{setting_name}}`
+
+- Change the keystore password:
+
+`elasticsearch-keystore passwd`
+
+- List all settings stored in the keystore:
+
+`elasticsearch-keystore list`
+
+- Upgrade the keystore format (after an Elasticsearch upgrade):
+
+`elasticsearch-keystore upgrade`