Backport of agent: Fix assignment of error when auto-reloading cert and key file changes. into release/1.14.x (#15772)

* backport of commit 7d0cf566ca

* backport of commit 024c8a84a6

* removing unused reference to pboperator

Co-authored-by: John Murret <john.murret@hashicorp.com>

.changelog/15769.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+agent: Fix assignment of error when auto-reloading cert and key file changes.
+```

agent/agent.go

@@ -4024,13 +4024,13 @@ func (a *Agent) reloadConfig(autoReload bool) error {
 			{a.config.TLS.HTTPS, newCfg.TLS.HTTPS},
 		} {
 			if f.oldCfg.KeyFile != f.newCfg.KeyFile {
-				a.configFileWatcher.Replace(f.oldCfg.KeyFile, f.newCfg.KeyFile)
+				err = a.configFileWatcher.Replace(f.oldCfg.KeyFile, f.newCfg.KeyFile)
 				if err != nil {
 					return err
 				}
 			}
 			if f.oldCfg.CertFile != f.newCfg.CertFile {
-				a.configFileWatcher.Replace(f.oldCfg.CertFile, f.newCfg.CertFile)
+				err = a.configFileWatcher.Replace(f.oldCfg.CertFile, f.newCfg.CertFile)
 				if err != nil {
 					return err
 				}