[REQ][ELIXIR] Use Tesla.Middleware.PathParams instead of string interpolation for path parameters

[marcowindt]

Is your feature request related to a problem? Please describe.

The Elixir generator interpolates path parameters directly into the URL string ("/companies/#{company_id}"). This means Tesla.Middleware.PathParams is a no-op even when configured, and middleware that depends on it — like opentelemetry_tesla — can't see the original path template.

In practice, this breaks OpenTelemetry span naming: since opts[:path_params] is never set, all spans fall back to just the HTTP method (GET, POST), making traces useless for distinguishing routes.

Describe the solution you'd like

Use the original OpenAPI path with {param} placeholders and pass parameters via opts[:path_params], so PathParams middleware actually does the substitution.

Example

Before:

|> url("/companies/#{company_id}")

After:

|> url("/companies/{companyId}")
|> add_path_params([{"companyId", company_id}])

Describe alternatives you've considered

Using custom templates via -t, which works but requires maintaining a couple of custom templates.

Happy to submit a PR for this.

Additional context

Only works when used with Tesla.Middleware.PathParams only, so that would be added to connection.ex.mustache.