Add contrast support for SSD1306

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

I have an esp32-c3 board with built-in SSD1306 OLED display. I would like to have a 'contrast' option to change how bright the screen displays text.
**Please describe your use case for this integration and alternatives you've tried:**

I would like to be able to have a dim display at night and a bright display in the day.
**Additional context**

I have found references to previous hacky solutions to contrast control for SSD1306 displays in the past, but AFAICT they have all been deprecated.
I found this blog which seemed to give useful detail on setting contrast for these sorts of displays: https://emalliab.wordpress.com/2025/02/12/esp32-c3-0-42-oled/

The request names an ESP32-C3 board and an SSD1306 OLED display but does not mention repository files, tests, or an implementation entry point. Start by locating the ESPHome component that handles SSD1306 displays and reviewing how its display settings are configured, then compare the linked blog's contrast details with the current behavior. Done means a defined contrast option supports dim and bright display use cases.

Written by the indexing model from the issue text.