v7.21.0 Add unmarshal json for template and InputOption for RichMenuAction

What's Changed

• Add unmarshal json for template by @yoshinobc in #346
• Add InputOption for RichMenuAction by @s-aska in #358

bug fix

• fix: Use POST method for Test Webhook endpoiont by @unnoy in #356

minors

• chore(deps): update actions/checkout action to v4 by @renovate in #354
• Fixed a small typo README.md by @IvanReyesO7 in #353
• chore: remove refs to deprecated io/ioutil by @testwill in #350
• update gihub action go matrix from 1.19 to 1.20.6 by @kkdai in #351
• Release 7.21.0 by @Yang-33 in #359

New Contributors

• @yoshinobc made their first contribution in #346
• @testwill made their first contribution in #350
• @IvanReyesO7 made their first contribution in #353
• @unnoy made their first contribution in #356
• @s-aska made their first contribution in #358

Full Changelog: v7.20.0...v7.21.0