feat: refactor platform authentication (#3758)

lib/config/index.js

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

lib/platform/azure/index.js

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

lib/platform/bitbucket-server/index.js

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

lib/platform/bitbucket/index.js

lib/platform/git/storage.ts

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/index.js

lib/util/host-rules.ts

lib/workers/global/autodiscover.js

lib/workers/global/index.js

lib/workers/repository/init/apis.js

test/config/index.spec.js

test/globals.js

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