feat: Support multiple configuration files (#396)

* Revert "Revert "feat: Support multiple configuration files" (#395)"

This reverts commit 87740e74a6.

* feat: Properly implement support for config directory

vendor/github.com/TwiN/deepmerge/README.md

@@ -0,0 +1,59 @@
+# deepmerge
+![test](https://github.com/TwiN/deepmerge/workflows/test/badge.svg?branch=master)
+
+Go library for deep merging YAML files.
+
+
+## Usage
+```go
+package main
+
+import (
+	"github.com/TwiN/deepmerge"
+)
+
+func main() {
+	dst := `
+debug: true
+client:
+  insecure: true
+users:
+  - id: 1
+    firstName: John
+    lastName: Doe
+  - id: 2
+    firstName: Jane
+    lastName: Doe`
+	src := `
+client:
+  timeout: 5s
+users:
+  - id: 3
+    firstName: Bob
+    lastName: Smith`
+
+	output, err := deepmerge.YAML([]byte(dst), []byte(src))
+	if err != nil {
+		panic(err)
+	}
+	println(string(output))
+}
+```
+
+Output:
+```yaml
+client:
+    insecure: true
+    timeout: 5s
+debug: true
+users:
+    - firstName: John
+      id: 1
+      lastName: Doe
+    - firstName: Jane
+      id: 2
+      lastName: Doe
+    - firstName: Bob
+      id: 3
+      lastName: Smith
+```