New API implementation: Routes API

[robery567]

Is your feature request related to a problem? Please describe.
It would be really helpful to directly implement the RoutesAPI into this package.

Describe the solution you'd like
I have realised the necessary modifications and I am considering opening a PR for it.

Describe alternatives you've considered
None.

Additional context
None

[usefulthink]

See here: #1105

The new routes API does have its own package here: https://github.com/googleapis/google-cloud-node/tree/main/packages/google-maps-routing and

[robery567]

I saw it, but as I already have this package implemented in one of our internal services, it was much easier to implement it directly in this package too, so we won't have to switch packages and implement a new one 😀.