Add a simple 'skip_initial' filter (#4582)

* Add a simple 'skip' filter

This filter simply skips the first `send_first_at` values, then passes
everything as-is. This is quite useful when you know the first few sensor
readings should be ignored.

Example YAML:

```yaml
sensor:
  - platform: sgp30
    id: mysensor_sgp30
    eco2:
      id: mysensor_sgp30_co2
      name: "eCO₂"
      accuracy_decimals: 0
      filters:
        - skip:
            send_first_at: 41
```

* Rename the filter to `skip_initial` and simplify the schema

New usage:

```yaml
      filters:
        - skip_initial: 41
```

* Apply clang-format

esphome/components/sensor/__init__.py

@@ -194,6 +194,7 @@ SensorPublishAction = sensor_ns.class_("SensorPublishAction", automation.Action)
 Filter = sensor_ns.class_("Filter")
 QuantileFilter = sensor_ns.class_("QuantileFilter", Filter)
 MedianFilter = sensor_ns.class_("MedianFilter", Filter)
+SkipInitialFilter = sensor_ns.class_("SkipInitialFilter", Filter)
 MinFilter = sensor_ns.class_("MinFilter", Filter)
 MaxFilter = sensor_ns.class_("MaxFilter", Filter)
 SlidingWindowMovingAverageFilter = sensor_ns.class_(
@@ -365,6 +366,11 @@ MIN_SCHEMA = cv.All(
 )
 
 
+@FILTER_REGISTRY.register("skip_initial", SkipInitialFilter, cv.positive_not_null_int)
+async def skip_initial_filter_to_code(config, filter_id):
+    return cg.new_Pvariable(filter_id, config)
+
+
 @FILTER_REGISTRY.register("min", MinFilter, MIN_SCHEMA)
 async def min_filter_to_code(config, filter_id):
     return cg.new_Pvariable(