Allow custom pin schema for Dallas component

**Describe the problem you have/What new integration you would like**

I would like to be able to use advanced `pin` configuration for the `dallas` component, including using `ignore_strapping_warning` and `pullup`.

**Please describe your use case for this integration and alternatives you've tried:**

I am using an ESP with the only external GPIO usable for Dallas DS18B20 being GPIO15.
GPIO15 is a bootstrap pin, and I get warnings about not using `ignore_strapping_warning`.
But the `dallas` component does not support advanced `pin` configuration.
I would also like to enable the internal pullup so that I don't need to use an external 4.7K resistor.

**Additional context**

Current config:

```yaml
# Use expansion slot Pin6 GPIO15 for Dallas
# https://esphome.io/components/sensor/dallas.html
dallas:
# TODO: How to add ignore_strapping_warning: true
# WARNING GPIO15 is a strapping PIN and should only be used for I/O with care.
- pin: GPIO15
update_interval: 5s
```

Desired config e.g.:
```yaml
# Use expansion slot Pin6 GPIO15 for Dallas
# https://esphome.io/components/sensor/dallas.html
dallas:
- pin:
number: GPIO15
pullup: true
ignore_strapping_warning: true
update_interval: 5s
```

Start with the Dallas component configuration and its existing pin handling. Check how nested GPIO pin options are represented, then verify that the YAML example is accepted and that both pull-up behavior and the strapping-pin warning setting work as requested.

Written by the indexing model from the issue text.