Refactor observability configuration and support files

- Introduced `filterCertificateSupportFiles` function to filter support files for certificates in `agent.go`.
- Updated placeholder constants in `config_version.go` to reflect changes from support directory to certificate directory.
- Modified tests in `https_phase1_test.go` to align with new directory structure and removed obsolete checks for observability Lua scripts.
- Removed observability assets from `openresty_observability_assets.go` and created a new file `observability_assets.go` in `atsf_agent/internal/nginx` to manage observability Lua scripts.
- Updated documentation to reflect changes in configuration paths for certificates and Lua scripts.
- Ensured that the agent writes to the new `cert_dir` and `lua_dir` instead of the old `support_dir`.

atsf_server/service/agent.go

@@ -191,6 +191,7 @@ func GetActiveConfigForAgent() (*AgentConfigResponse, error) {
 			return nil, err
 		}
 	}
+	supportFiles = filterCertificateSupportFiles(supportFiles)
 	slog.Debug("agent fetched active config", "version", version.Version, "checksum", version.Checksum)
 	return &AgentConfigResponse{
 		Version:        version.Version,
@@ -203,6 +204,21 @@ func GetActiveConfigForAgent() (*AgentConfigResponse, error) {
 	}, nil
 }
 
+func filterCertificateSupportFiles(files []SupportFile) []SupportFile {
+	if len(files) == 0 {
+		return nil
+	}
+	filtered := make([]SupportFile, 0, len(files))
+	for _, file := range files {
+		path := strings.ToLower(strings.TrimSpace(file.Path))
+		switch {
+		case strings.HasSuffix(path, ".crt"), strings.HasSuffix(path, ".key"), strings.HasSuffix(path, ".pem"):
+			filtered = append(filtered, file)
+		}
+	}
+	return filtered
+}
+
 func ReportApplyLog(payload ApplyLogPayload) (*model.ApplyLog, error) {
 	now := time.Now()
 	payload.NodeID = strings.TrimSpace(payload.NodeID)