Add is_indoors roadFlag

[Rachmanin0xFF]

Description

Adds the road flag is_indoors to handle the inclusion of indoor road segments, which have been filtered until now as a result of https://github.com/OvertureMaps/tf-transportation/issues/83.

These segments are mostly footways and steps, and could be useful for indoor routing.

Reference

1. https://github.com/OvertureMaps/tf-transportation/issues/421#event-16355827551
2. https://github.com/OvertureMaps/tf-transportation/pull/428
3. https://github.com/OvertureMaps/tf-transportation/issues/83

Testing

Testing completed during implementation

Checklist

1. Add relevant examples.
2. Add relevant counterexamples.
3. Update any counterexamples that became obsolete. For example, if a counterexample uses property A but is not intended to test property A's validity, and you made a schema change that invalidates property A in that counterexample, fix the counterexample to align it with your schema change.
4. Update in-schema documentation using plain English written in complete sentences, if an update is required.
5. Update Docusaurus documentation, if an update is required.
6. Review change with Overture technical writer to ensure any advanced documentation needs will be taken care of, unless the change is trivial and would not affect the documentation.

Documentation website

Update the hyperlink below to put the pull request number in.

Docs preview for this PR.