Avg column was being added at every rendering, if the table was empty.
Now the column will be added once as an initialization when selecting a
'timeseries_aggregations' transform.

ref #3302

ref #7934 
ref #7968
ref #3164

ref #8277, ref #8250, ref #8262, ref #8165, ref #8093, ref #8056, ref #8043, ref #7970, ref #7914, ref #7864, ref #7750, ref #7740, ref #7697, ref #7619, ref #5619, ref #4030, ref #5278, ref #3302, ref #2524

fix: fixed slow down issue in table panel by removing the fillter null values feature (#7602), not sure the filter null values is a good table option, should be done in metric query, fixes #8234

The parameter fielddata_fields is deprecated and removed in 5.0 https://github.com/elastic/elasticsearch/issues/19027