Elasticsearch: Add versions supporting 7.6 to matrix
Elasticsearch: Add versions supporting 7.6 to matrix

Change-Id: I01a276e3de895b2ac5491f24fa0bc27de53a35c5

GerritCodeReview/homepage,GerritCodeReview/homepage,GerritCodeReview/homepage,GerritCodeReview/homepage,GerritCodeReview/homepage