Implement methods for user secrets management

This commit introduces internal/juju/userSecret and adds method to add user secrets.

internal/juju/userSecret.go

@@ -0,0 +1,78 @@
+// Copyright 2024 Canonical Ltd.
+// Licensed under the Apache License, Version 2.0, see LICENCE file for details.
+
+package juju
+
+import (
+	"strings"
+
+	"github.com/juju/juju/api/client/secrets"
+)
+
+type userSecretClient struct {
+	SharedClient
+}
+
+type AddUserSecretInput struct {
+	ModelName   string
+	Name        string
+	Value       string
+	Description string
+}
+
+type AddUserSecretOutput struct {
+	SecretURI string
+}
+
+type ReadUserSecretInput struct {
+	ModelName string
+	Name      string
+}
+
+type UpdateUserSecretInput struct {
+	ModelName string
+	Name      string
+	Value     string
+}
+
+type RemoveUserSecretInput struct {
+	ModelName string
+	Name      string
+}
+
+func newUserSecretClient(sc SharedClient) *userSecretClient {
+	return &userSecretClient{
+		SharedClient: sc,
+	}
+}
+
+func (c *userSecretClient) AddUserSecret(input *AddUserSecretInput) (*AddUserSecretOutput, error) {
+	conn, err := c.GetConnection(&input.ModelName)
+	if err != nil {
+		return nil, err
+	}
+	defer func() { _ = conn.Close() }()
+
+	client := secrets.NewClient(conn)
+	secretURI, err := client.CreateSecret(input.Name, input.Description, parseSecretValueStringToMap(input.Value))
+	if err != nil {
+		return nil, err
+	}
+	return &AddUserSecretOutput{
+		SecretURI: secretURI,
+	}, nil
+}
+
+func parseSecretValueStringToMap(input string) map[string]string {
+	result := make(map[string]string)
+	pairs := strings.Split(input, " ")
+
+	for _, pair := range pairs {
+		kv := strings.Split(pair, "=")
+		if len(kv) == 2 {
+			result[kv[0]] = kv[1]
+		}
+	}
+
+	return result
+}