feat: add strings dictionary for english

src/app/strings.ts

@@ -0,0 +1,13 @@
+export const strings = Object.freeze({
+  add: 'add',
+  addContact: 'add a contact',
+  allFieldRequired: 'all fields are required',
+  company: 'company',
+  contactList: 'contact list',
+  name: 'name',
+  phone: 'phone',
+  errorMessageRequired: 'This field is required.',
+  errorMessageMaxLength: (maxLen: number) => `Must be ${maxLen} characters or fewer.`,
+  errorMessageMinLength: (minLen: number) => `Must be at least ${minLen} characters long.`,
+  errorMessagePhonePattern: `Valid format: + (optional) plus 12 to 15 digits`,
+});