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

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.

Start with the Elixir generator's connection.ex.mustache template and inspect how generated requests currently build URLs and pass options. Compare the generated client with Tesla.Middleware.PathParams expectations. Done means OpenAPI path placeholders and opts[:path_params] reach the middleware so route-specific tracing can use the original template.