Explain order in the readme and introduce IRange interface

Author: Tomas Winkler

README.md

@@ -96,7 +96,7 @@ The supported commands are divided into groups according to their target, at thi
   * The file is stored in the `Migrations` directory within the root of your repository. 
   * Add your migration script in the body of the `run` function using the [Kontent Management SDK](https://github.com/Kentico/kontent-management-sdk-js) that was injected via the `apiClient` parameter.
   * To choose between JavaScript and TypeScript when generating the script file, use the `--template-type` option, such as `--template-type "javascript"`.
-  * The migration template contains an `order` property that is used to run a batch of migrations in the specified order.
+  * The migration template contains an `order` property that is used to run a batch of migrations (range or all) in the specified order. The `order` must be a unique, positive integer or zero. There may be gaps between migrations, for example, the following sequence is perfectly fine 0,3,4,5,10
 
     ```typescript
     // Example migration template 

src/cmds/migration/run.ts

@@ -6,6 +6,7 @@ import { environmentConfigExists, getEnvironmentsConfig } from '../../utils/envi
 import { createManagementClient } from '../../managementClientFactory';
 import { loadMigrationsExecutionStatus } from '../../utils/statusManager';
 import { IMigration } from '../../models/migration';
+import { IRange } from '../../models/range';
 
 const runMigrationCommand: yargs.CommandModule = {
     command: 'run',
@@ -182,15 +183,20 @@ const runMigrationCommand: yargs.CommandModule = {
     },
 };
 
-export const getRange = (range: string): [number, number] | null => {
+export const getRange = (range: string): IRange | null => {
     const match = range.match(/^([0-9]+):([0-9]+)$/);
     if (!match) {
         return null;
     }
     const from = Number(match[1]);
     const to = Number(match[2]);
 
-    return from <= to ? [from, to] : null;
+    return from <= to
+        ? {
+              from,
+              to,
+          }
+        : null;
 };
 
 const checkForDuplicates = (migrationsToRun: IMigration[]): void => {
@@ -204,11 +210,11 @@ const checkForDuplicates = (migrationsToRun: IMigration[]): void => {
     }
 };
 
-const getMigrationsByRange = (migrationsToRun: IMigration[], range: [number, number]): IMigration[] => {
+const getMigrationsByRange = (migrationsToRun: IMigration[], range: IRange): IMigration[] => {
     const migrations: IMigration[] = [];
 
     for (const migration of migrationsToRun) {
-        if (migration.module.order >= range[0] && migration.module.order <= range[1]) {
+        if (migration.module.order >= range.from && migration.module.order <= range.to) {
             migrations.push(migration);
         }
     }

src/models/range.ts

@@ -0,0 +1,4 @@
+export interface IRange {
+    from: number;
+    to: number;
+}

src/tests/invalidOrderMigration.test.ts

@@ -53,7 +53,13 @@ describe('Detection of invalid orders', () => {
             },
             {
                 module: {
-                    order: 3,
+                    order: 6,
+                    name: 'test',
+                },
+            },
+            {
+                module: {
+                    order: 7,
                     name: 'test',
                 },
             },