Update dependency config to v4

Author: renovate[bot]

package.json

@@ -40,7 +40,7 @@
     "@hmcts/properties-volume": "^1.0.0",
     "applicationinsights": "2.9.8",
     "body-parser": "^2.2.1",
-    "config": "^1.26.1",
+    "config": "^4.0.0",
     "connect-timeout": "^1.9.0",
     "cookie": "^0.7.0",
     "cross-env": "^5.2.0",

yarn.lock

@@ -1550,7 +1550,7 @@ __metadata:
     chai: "npm:^4.3.6"
     chai-arrays: "npm:^2.0.0"
     chai-http: "npm:^4.0.0"
-    config: "npm:^1.26.1"
+    config: "npm:^4.0.0"
     connect-timeout: "npm:^1.9.0"
     cookie: "npm:^0.7.0"
     cross-env: "npm:^5.2.0"
@@ -1827,12 +1827,12 @@ __metadata:
   languageName: node
   linkType: hard
 
-"config@npm:^1.26.1":
-  version: 1.31.0
-  resolution: "config@npm:1.31.0"
+"config@npm:^4.0.0":
+  version: 4.3.0
+  resolution: "config@npm:4.3.0"
   dependencies:
-    json5: "npm:^1.0.1"
-  checksum: 10/cb53d3f84e13ad6dc531a6492ead2a86ea063684a1a5ed9cd204018ee8d444751840039d6e69f42263506367f613e5ed010aa276d44f469663ed56331add7b88
+    json5: "npm:^2.2.3"
+  checksum: 10/e62b05aa9dc0e44de40d4027d36fd15e5dabaf933d58446bfed2045a0fb56860af246c67fb1057a5956592399497ff0c5b41010b1ac1c6a86077a38930ea33b3
   languageName: node
   linkType: hard