refactor: endpoints -> hostRules (#2509)

lib/config/cli.js

lib/config/definitions.js

lib/config/env.js

lib/config/index.js

lib/config/migration.js

lib/datasource/docker.js

lib/datasource/npm.js

lib/manager/composer/lock-file.js

lib/platform/bitbucket/bb-got-wrapper.js

lib/platform/bitbucket/index.js

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

lib/platform/github/index.js

lib/platform/gitlab/gl-got-wrapper.js

lib/platform/gitlab/index.js

lib/platform/vsts/index.js

lib/platform/vsts/vsts-got-wrapper.js

lib/util/host-rules.js

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

test/config/__snapshots__/env.spec.js.snap

test/config/__snapshots__/migration.spec.js.snap