feat(presets): add support for local presets (#5814)

docs/usage/config-presets.md

lib/config/common.ts

lib/config/index.ts

lib/config/presets/__snapshots__/index.spec.ts.snap

lib/config/presets/__snapshots__/local.spec.ts.snap

lib/config/presets/github.spec.ts

lib/config/presets/github.ts

lib/config/presets/gitlab.spec.ts

lib/config/presets/gitlab.ts

lib/config/presets/index.spec.ts

lib/config/presets/index.ts

lib/config/presets/local.spec.ts

lib/config/presets/local.ts

lib/config/validation.ts

lib/platform/azure/index.ts

lib/platform/bitbucket-server/index.ts

lib/platform/gitea/index.ts

lib/platform/github/index.ts

lib/platform/gitlab/index.ts

lib/util/url.ts