feat: Add support for Integration Mappings API

[coveralls]

Pull Request Test Coverage Report for Build 5145105390

• 65 of 68 (95.59%) changed or added relevant lines in 4 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.008%) to 86.33%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/commands/integration-mappings/slack/index.js	18	19	94.74%
src/commands/integration-mappings/slack/create.js	20	22	90.91%
<!--	Total:	65	68	95.59%	-->

Totals
Change from base Build 5069082473:	0.008%
Covered Lines:	4116
Relevant Lines:	4616

---

💛 - Coveralls