Refactor _getEtag to get etag from gzip instead of buffer #270

Job	Run time
ESP32 (arduino-cli) - Release	23m 8s
ESP32 (arduino-cli) - Dev	24m 40s
ESP32 (pio) - Arduino 2 (esp32-s3-devkitc-1)	11m 28s
ESP32 (pio) - Arduino 2 (esp32-s2-saola-1)	11m 24s
ESP32 (pio) - Specific Envs (ci-arduino-3-no-json)	20m 41s
ESP32 (pio) - Arduino 2 (esp32-c3-devkitc-02)	10m 27s
ESP32 (pio) - Arduino Latest (esp32-s2-saola-1)	18m 20s
ESP32 (pio) - Arduino Latest (esp32dev)	17m 34s
ESP32 (pio) - Arduino Latest (esp32-c3-devkitc-02)	16m 37s
ESP32 (pio) - Arduino 3 (esp32-c3-devkitc-02)	21m 33s
ESP32 (pio) - Arduino Latest (esp32-c6-devkitc-1)	17m 11s
ESP32 (pio) - Arduino 2 (esp32dev)	11m 11s
ESP32 (pio) - Arduino Latest (esp32-s3-devkitc-1)	18m 49s
ESP32 (pio) - Arduino 3 (esp32-p4)	21m 33s
ESP32 (pio) - Arduino 3 (esp32-s2-saola-1)	22m 34s
ESP32 (pio) - Arduino Latest (esp32-h2-devkitm-1)	14m 36s
ESP32 (pio) - Arduino 3 (esp32-s3-devkitc-1)	23m 12s
ESP32 (pio) - Arduino 3 (esp32dev)	22m 31s
ESP32 (pio) - Specific Envs (ci-arduino-rc-asynctcp)	20m 53s
ESP32 (pio) - Arduino 3 (esp32-c6-devkitc-1)	22m 6s
ESP32 (pio) - Arduino 3 (esp32-h2-devkitm-1)	18m 57s
	6h 29m 25s

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