fix(thermostat): MinSetpoint­DeadBand should be SignedTemperature (CON-1634)

[andylinpersonal]

Description

The attribute MinSetpoint­DeadBand in Thermostat cluster should be a SignedTemperature (int8_t) value, which is in 0.1°C and constrained to [0, +127].
But the function esp_matter::cluster::thermostat::add_bounds_cb erroneously uses TemperatureDifference (int16_t) value with wrong constraint [0, +1270].

Testing

The following snippets should not report the following error:
"Cannot set bounds because of val type mismatch: expected: 7, min: 9, max: 9"

	esp_matter::cluster_t* thermostat_cluster = /* your cluster */;
	esp_matter::cluster::thermostat::feature::auto_mode::config_t auto_config;
	auto_config.min_setpoint_dead_band = 25;
	esp_matter::cluster::thermostat::feature::auto_mode::add(thermostat_cluster, &auto_config);

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