Update to golang 1.16.5/1.15.13

[michel-laterman]

Update the versions of golang used to the latest patches which contain security fixes

• Update crossbuild images
• Update beats
• Update fleet-server
• ping APM

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[michel-laterman]

@simitt, The images to update to go 1.16.5 and 1.15.13 are available. I didn't have any issues when updating beats 7.13.2 to 1.15.13; however due to a change in the go mod download command there may be issues with the update to 1.16.5

[simitt]

thanks for the ping, we will try to update when the beats PR is merged.