DS1307 - Add support for SRAM

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

The DS1307 has 56 bytes of NVRAM, with unlimited write cycles, that could be useful for saving power-on information without using the FLASH on the ESP chip, which has limited write cycles.
**Please describe your use case for this integration and alternatives you've tried:**

Storing the current state of a component on the ESP FLASH memory limits the amount of writes before the FLASH memory becomes unusable, and the ESP chip needs to be replaced. By storing the component state, or any other variable information in a battery-backed NVRAM, the writes can be indefinite, and therefore the information can be saved in real-time without any problems.
**Additional context**

ESPHome already has support for the clock on the DS1307 chip, it would only need the RAM support added.

Start by locating ESPHome's existing DS1307 clock integration and inspect how the device is represented. Determine how its 56-byte battery-backed NVRAM should be exposed for storing component state or other variables, then verify that the resulting support avoids using ESP flash for those writes.

Written by the indexing model from the issue text.