Create the MD5 sum on firmware compilation

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

The Feature request that I'm requesting/suggesting is to generate the MD5 checksum, save it in a file on the same folder of the firmware, in order to enable this* endpoint to expose it on the esphome devices and successfully complete the ota update using the http request platform:
*
```
https://**OMITTED**/download.bin?configuration=multisensor-2410-shtc3.yaml&file=MD5.ota.txt
```

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

Hi!. I plan to create 8 device identical to each other. I don't want to create 8 different firmware configuration and 8 different firmware, but 1 config and 1 firmware only.

In order to do this and keeping the ota update available, I plan to use the http request platform instead the default esphome platform and use the esphome dashboard itself to provide the firmware. (the dashboard has a nice endpoint to download the firmware and it's always available on my network).
The problem is the MD5 checksum url because currently esphome require it on this platform, but the esphome doesn't calc it and doesn't store it in any file.

**Additional context**

Start by tracing the HTTP request platform and the ESPHome dashboard firmware download endpoint described in the request. Check how firmware compilation artifacts are stored, then determine where the checksum file would belong. Done means compilation produces an MD5 file beside the firmware and the dashboard can serve it through the requested URL.

Written by the indexing model from the issue text.