feat(github): convert to typescript (#3975)

.babelrc

.vscode/launch.json

lib/datasource/github/index.js

lib/platform/github/gh-got-wrapper.ts

lib/platform/github/index.ts

lib/types.d.ts

lib/workers/pr/changelog/release-notes.js

lib/workers/pr/changelog/source-github.js

package.json

test/datasource/github.spec.js

test/platform/__snapshots__/index.spec.js.snap

test/platform/github/__snapshots__/index.spec.ts.snap

test/platform/github/gh-got-wrapper.spec.ts

test/platform/github/index.spec.ts

test/platform/index.spec.js

test/workers/pr/changelog/index.spec.js

yarn.lock