Configure Dependabot for Jest dependencies

[ybiquitous]

Which issue, if any, is this issue related to?

Closes #429

Is there anything in the PR that needs further explanation?

We have to bump Jest-related packages at the same time, especially for major updates.

Also, this PR will reduce the number of Dependabot PRs.

---

We can see the related dependencies in package.json as below:

$ git grep 'jest' package.json
package.json:225:    "@types/jest": "^27.0.3",
package.json:240:    "jest": "^27.4.3",
package.json:241:    "jest-runner-vscode": "^2.1.0",
package.json:253:    "ts-jest": "^27.0.7",
package.json:275:    "test": "npm run build-bundle && jest",
package.json:276:    "test:e2e": "npm run build-bundle && jest --projects test/e2e",
package.json:277:    "test:integration": "jest --projects test/integration",
package.json:278:    "test:unit": "jest --projects test/unit",

[adalinesimonian]

LGTM