golang: v↑ go1.14 (1.14.12 -> 1.14.15)

Going Go1.14.12 -> Go1.14.15 brings in fixes to compiler, runtime, standard
library and build security.

https://golang.org/doc/devel/release.html#go1.14.minor

Tested on helloworld SR (by adjusting it to use go1.14 instead of go1.15)

Go1.14.15 is the last Go1.14.x release, because, after Go1.16 was released, Go1.14
becomes end-of-life and will not receive any updates nor fixes for security bugs.

/cc @jerome (for theia which is on go1.14)
/cc @luke (for caddy which is on go1.14)

/cc @tomo, @alain.takoudjou (for galene which is still on EOL go1.13)
/cc @alain.takoudjou (for replication-manager which is still on EOL go1.13)
/cc @alain.takoudjou (for restic which is still on EOL go1.13)

/cc @jerome, @alain.takoudjou (for gitlab which is still on EOL go1.12)
/cc @jerome (for grafana which is still on EOL go1.12)