slog migration: service layer + subsystem libraries (#40661)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #40540 

# Checklist for submitter

- [ ] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
  - Changes present in previous PR

## Testing

- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Refactor**
* Updated internal logging infrastructure to improve consistency and
maintainability across the application.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

cmd/fleetctl/integrationtest/gitops/gitops_enterprise_integration_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"log/slog"
 	"maps"
 	"net/http"
 	"net/http/httptest"
@@ -110,7 +111,7 @@ func (s *enterpriseIntegrationGitopsTestSuite) SetupSuite() {
 		SCEPStorage:            scepStorage,
 		Pool:                   redisPool,
 		APNSTopic:              "com.apple.mgmt.External.10ac3ce5-4668-4e58-b69a-b2b5ce667589",
-		SCEPConfigService:      eeservice.NewSCEPConfigService(logging.NewLogfmtLogger(os.Stdout), nil),
+		SCEPConfigService:      eeservice.NewSCEPConfigService(slog.New(slog.NewTextHandler(os.Stdout, nil)), nil),
 		DigiCertService:        digicert.NewService(),
 		SoftwareTitleIconStore: softwareTitleIconStore,
 	}