TRA-3860 create main configmap for agent and tappers (#410)

* WIP

* Update options.go and serializable_regexp.go

* Update go.sum, go.sum, and 4 more files...

* Update go.sum, go.sum, and 4 more files...

* Update config.go and serializable_regexp.go

* Update config.go, config.json, and test.go

* Update tapRunner.go and provider.go

* Update provider.go

* Update tapRunner.go and provider.go

* Update config.json and test.go

* Update contract_validation.go, config.go, and 2 more files...

* Update main.go

* Update rulesHTTP.go

* Update config.go, size_enforcer.go, and 5 more files...

* Update config.go and config.go

Co-authored-by: Rami Berman <rami.berman@up9.com>

agent/pkg/config/config.go

@@ -0,0 +1,57 @@
+package config
+
+import (
+	"encoding/json"
+	"fmt"
+	"github.com/up9inc/mizu/shared"
+	"io/ioutil"
+	"os"
+)
+
+// these values are used when the config.json file is not present
+const (
+	defaultMaxDatabaseSizeBytes int64  = 200 * 1000 * 1000
+	defaultRegexTarget          string = ".*"
+)
+
+var Config *shared.MizuAgentConfig
+
+func LoadConfig() error {
+	if Config != nil {
+		return nil
+	}
+	filePath := fmt.Sprintf("%s%s", shared.ConfigDirPath, shared.ConfigFileName)
+
+	content, err := ioutil.ReadFile(filePath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return applyDefaultConfig()
+		}
+		return err
+	}
+
+	if err = json.Unmarshal(content, &Config); err != nil {
+		return err
+	}
+	return nil
+}
+
+func applyDefaultConfig() error {
+	defaultConfig, err := getDefaultConfig()
+	if err != nil {
+		return err
+	}
+	Config = defaultConfig
+	return nil
+}
+
+func getDefaultConfig() (*shared.MizuAgentConfig, error) {
+	regex, err := shared.CompileRegexToSerializableRegexp(defaultRegexTarget)
+	if err != nil {
+		return nil, err
+	}
+	return &shared.MizuAgentConfig{
+		TapTargetRegex: *regex,
+		MaxDBSizeBytes: defaultMaxDatabaseSizeBytes,
+	}, nil
+}