[ci] add missing artifacts in buildkite

[SylvainJuge]

Not all the published artifacts were included in the buildkite result, thus this PR fixes that.

Finding which gradle modules/projects needs to be used here is quite straightforward by using the following command:

find . -name 'build.gradle.kts'|xargs grep 'sign-and-publish-conventions'|column -t

Which here provides:

./inferred-spans/build.gradle.kts:  id("elastic-otel.sign-and-publish-conventions")
./common/build.gradle.kts:          id("elastic-otel.sign-and-publish-conventions")
./agentextension/build.gradle.kts:  id("elastic-otel.sign-and-publish-conventions")
./agent/build.gradle.kts:           id("elastic-otel.sign-and-publish-conventions")