Fix lookup issues with inputs.d fragment yml

The Elastic Agent was looking next to the binary for the `inputs.d`
folder instead it should look up into the `Home` folder where
the Elastic Agent symlink is located.

Fixes: elastic#663

internal/pkg/agent/application/paths/files.go

@@ -32,6 +32,9 @@ const defaultAgentStateStoreYmlFile = "state.yml"
 // defaultAgentStateStoreFile is the file that will contain the action that can be replayed after restart encrypted.
 const defaultAgentStateStoreFile = "state.enc"
 
+// defaultInputDPath return the location of the inputs.d.
+const defaultInputsDPath = "inputs.d"
+
 // AgentConfigYmlFile is a name of file used to store agent information
 func AgentConfigYmlFile() string {
 	return filepath.Join(Config(), defaultAgentFleetYmlFile)
@@ -82,3 +85,8 @@ func AgentStateStoreYmlFile() string {
 func AgentStateStoreFile() string {
 	return filepath.Join(Home(), defaultAgentStateStoreFile)
 }
+
+// AgentInputsDPath is directory that contains the fragment of inputs yaml for K8s deployment.
+func AgentInputsDPath() string {
+	return filepath.Join(Home(), defaultInputsDPath)
+}

internal/pkg/agent/configuration/settings.go

@@ -7,6 +7,7 @@ package configuration
 import (
 	"path/filepath"
 
+	"github.com/elastic/elastic-agent/internal/pkg/agent/application/paths"
 	"github.com/elastic/elastic-agent/internal/pkg/artifact"
 	monitoringCfg "github.com/elastic/elastic-agent/internal/pkg/core/monitoring/config"
 	"github.com/elastic/elastic-agent/internal/pkg/core/process"
@@ -16,7 +17,7 @@ import (
 )
 
 // ExternalInputsPattern is a glob that matches the paths of external configuration files.
-var ExternalInputsPattern = filepath.Join("inputs.d", "*.yml")
+var ExternalInputsPattern = filepath.Join(paths.AgentInputsDPath(), "*.yml")
 
 // SettingsConfig is an collection of agent settings configuration.
 type SettingsConfig struct {