[jaeger-v2] Add validation and comments to memory storage config (#5925)

## Which problem is this PR solving?
- Resolves #5923

## Description of the changes
- Implemented `Validate` method for `Configuration` struct for memory
storage
- Created [migration
doc](https://docs.google.com/document/d/1w3z2hhxXAMLbuWsyyigUUMNSfflw4uayUERqHf45Dks/edit?usp=sharing)
from v1 to v2

## How was this change tested?
- Added unit tests for the new method

## Checklist
- [x] I have read
https://github.com/jaegertracing/jaeger/blob/master/CONTRIBUTING_GUIDELINES.md
- [x] I have signed all commits
- [x] I have added unit tests for the new functionality
- [x] I have run lint and test steps successfully
  - for `jaeger`: `make lint test`
  - for `jaeger-ui`: `yarn lint` and `yarn test`

---------

Signed-off-by: Mahad Zaryab <mahadzaryab1@gmail.com>
Signed-off-by: Yuri Shkuro <yurishkuro@users.noreply.github.com>
Co-authored-by: Yuri Shkuro <yurishkuro@users.noreply.github.com>

plugin/storage/memory/config.go

@@ -3,7 +3,17 @@
 
 package memory
 
-// Configuration describes the options to customize the storage behavior
+import "github.com/asaskevich/govalidator"
+
+// Configuration describes the options to customize the storage behavior.
 type Configuration struct {
+	// MaxTraces is the maximum amount of traces to store in memory.
+	// If multi-tenancy is enabled, this limit applies per tenant.
+	// Zero value (default) means no limit (Warning: memory usage will be unbounded).
 	MaxTraces int `mapstructure:"max_traces"`
 }
+
+func (c *Configuration) Validate() error {
+	_, err := govalidator.ValidateStruct(c)
+	return err
+}

plugin/storage/memory/config_test.go

@@ -0,0 +1,35 @@
+// Copyright (c) 2024 The Jaeger Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+package memory
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestValidate_DoesNotReturnErrorWhenValid(t *testing.T) {
+	tests := []struct {
+		name   string
+		config *Configuration
+	}{
+		{
+			name:   "non-required fields not set",
+			config: &Configuration{},
+		},
+		{
+			name: "all fields are set",
+			config: &Configuration{
+				MaxTraces: 100,
+			},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			err := test.config.Validate()
+			require.NoError(t, err)
+		})
+	}
+}