Add API specs for OpenID Connect APIs

rest-api-spec/src/main/resources/rest-api-spec/api/security.oidc_authenticate.json

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+{
+  "security.oidc_authenticate":{
+    "documentation":{
+      "url":"https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-oidc-authenticate.html",
+      "description":"Exchanges an OpenID Connection authentication response message for an Elasticsearch access token and refresh token pair"
+    },
+    "stability":"stable",
+    "visibility":"public",
+    "headers":{
+      "accept": [ "application/json"],
+      "content_type": ["application/json"]
+    },
+    "url":{
+      "paths":[
+        {
+          "path":"/_security/oidc/authenticate",
+          "methods":[
+            "POST"
+          ]
+        }
+      ]
+    },
+    "body":{
+      "description":"The OpenID Connect response to authenticate",
+      "required":true
+    }
+  }
+}

rest-api-spec/src/main/resources/rest-api-spec/api/security.oidc_logout.json

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+{
+  "security.oidc_logout":{
+    "documentation":{
+      "url":"https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-oidc-logout.html",
+      "description":"Invalidates a refresh token and access token that was generated from the OpenID Connect Authenticate API"
+    },
+    "stability":"stable",
+    "visibility":"public",
+    "headers":{
+      "accept": [ "application/json"],
+      "content_type": ["application/json"]
+    },
+    "url":{
+      "paths":[
+        {
+          "path":"/_security/oidc/logout",
+          "methods":[
+            "POST"
+          ]
+        }
+      ]
+    },
+    "body":{
+      "description":"Access token and refresh token to invalidate",
+      "required":true
+    }
+  }
+}

rest-api-spec/src/main/resources/rest-api-spec/api/security.oidc_prepare_authentication.json

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+{
+  "security.oidc_prepare_authentication":{
+    "documentation":{
+      "url":"https://www.elastic.co/guide/en/elasticsearch/reference/current/security-api-oidc-prepare-authentication.html",
+      "description":"Creates an OAuth 2.0 authentication request as a URL string"
+    },
+    "stability":"stable",
+    "visibility":"public",
+    "headers":{
+      "accept": [ "application/json"],
+      "content_type": ["application/json"]
+    },
+    "url":{
+      "paths":[
+        {
+          "path":"/_security/oidc/prepare",
+          "methods":[
+            "POST"
+          ]
+        }
+      ]
+    },
+    "body":{
+      "description":"The OpenID Connect authentication realm configuration",
+      "required":true
+    }
+  }
+}