compress firmware bin with gzip for ota

[sVnsation]

Unfortunately, more than 50% is occupied in the version with 1M Flash:
Flash: [===== ] 50.6% (used 484985 bytes from 958448 bytes)
However, OTA is still possible thanks to the gzip compression of the firmware.
This PR also generates gzip compressed .bin.gz files for firmware ota.

The workflow runs successfully and generates .bin.gz files
example: https://github.com/sVnsation/ahoy/actions

[sVnsation]

Additional Information about gzip ota:
"ESP8266 Arduino framework v2.7.0 default bootloader added support for gzipped OTA updates here: esp8266/Arduino#6820
The compressed firmware image is then stored by the OTA backend on the flash. When the ESP is rebooted to apply the new firmware, the bootloader decompresses the image and writes it to the correct flash location."
Source: esphome/feature-requests#819