feat: Add a changelog for the v5

aws/logs_monitoring/CHANGELOG.md

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+# Datadog Lambda Forwarder Changelog
+
+## v5.0.0 - BREAKING CHANGES
+
+### Overview
+
+Version 5.0.0 of the Datadog Lambda Forwarder introduces several breaking changes that remove deprecated features and improve log filtering behavior. This release introduces a new way to enrich your logs with tags that will reduce AWS Lambda related cost (S3, KMS and Lambda).
+
+### New Features
+
+#### 1. Backend Storage Tag Enrichment
+
+**Added:**
+
+- New `DD_ENRICH_S3_TAGS` / `DdEnrichS3Tags` parameter (default: `true`)
+- New `DD_ENRICH_CLOUDWATCH_TAGS` / `DdEnrichCloudwatchTags` parameter (default: `true`)
+- These instruct the Datadog backend to automatically enrich logs with resource tags **after ingestion**
+- New cloudwatch tags can appear on logs, check your Datadog log index configuration to ensure smooth transition.
+
+**Benefits:**
+
+- **Reduces forwarder cost** and execution time
+- Provides the same tag enrichment as `DdFetchS3Tags` and `DdFetchLogGroupTags`
+- Requires [Resource Collection](https://docs.datadoghq.com/integrations/amazon-web-services/#resource-collection) enabled in your AWS integration
+
+**Deprecation Notice:**
+
+- `DdFetchS3Tags` is now marked as **DEPRECATED** in favor of `DdEnrichS3Tags`
+- `DdFetchLogGroupTags` is now marked as **DEPRECATED** in favor of `DdEnrichCloudwatchTags`
+- `DD_FETCH_S3_TAGS` now defaults to `false` (previously `true`)
+
+---
+
+### Breaking Changes
+
+#### 1. Changed Regex Matching Behavior for Log Filtering
+
+**What Changed:**
+
+- `IncludeAtMatch` / `INCLUDE_AT_MATCH` and `ExcludeAtMatch` / `EXCLUDE_AT_MATCH` regex patterns now match **only against the log message** itself
+- Previously, these patterns matched against the **entire JSON-formatted log**
+
+**Migration Required:**
+
+- **Review and update your filtering regex patterns**
+- If your patterns relied on matching against JSON structure or metadata fields, they will need to be rewritten
+- Example changes needed:
+    - **Before (v4)**: `\"awsRegion\":\"us-east-1\"` (matched JSON with escaped quotes)
+    - **After (v5)**: `"awsRegion":"us-east-1"` (matches the message content directly)
+- Patterns that matched the `message` field content should continue to work with minimal changes
+
+---
+
+#### 2. Removed TCP Transport Support
+
+**What Changed:**
+
+- Removed the `DD_USE_TCP` / `DdUseTcp` environment variable and parameter
+- Deleted the TCP client implementation
+- All logs now **must** be sent via HTTP/HTTPS
+
+**Migration Required:**
+
+- Remove any configuration setting `DD_USE_TCP=true` or `DdUseTcp=true`
+- The forwarder will now exclusively use HTTP transport
+- If you were using TCP with custom ports (10516), these configurations will be ignored
+- The default HTTP endpoint is now `http-intake.logs.<DD_SITE>` on port 443
+
+---
+
+#### 3. Removed Deprecated PrivateLink Environment Variable
+
+**What Changed:**
+
+- Removed the `DD_USE_PRIVATE_LINK` / `DdUsePrivateLink` environment variable and parameter
+
+**Migration Required:**
+
+- Remove any configuration setting `DD_USE_PRIVATE_LINK=true`
+- **AWS PrivateLink is still fully supported**, but you must follow [PrivateLink documentation](https://docs.datadoghq.com/agent/guide/private-link/):
+    1. Set up VPC endpoints for `api`, `http-logs.intake`, and `trace.agent` as documented
+    2. Configure the forwarder with `DdUseVPC=true`
+    3. Set `VPCSecurityGroupIds` and `VPCSubnetIds`
+
+**Why This Changed:**
+
+- The variable was previously deprecated but not removed from past versions.
+
+---
+
+### Upgrade Instructions
+
+Follow the usual [documentation](https://docs.datadoghq.com/logs/guide/forwarder/?tab=cloudformation#upgrade-to-a-new-version) about upgrading your Lambda Forwarder.
+
+#### Pre-Upgrade Checklist
+
+1. **Verify you're not using TCP transport:**
+
+    ```bash
+    aws lambda get-function-configuration --function-name "<YOUR_FORWARDER>" --query 'Environment.Variables.DD_USE_TCP'
+    ```
+
+2. **Verify you're not using the deprecated PrivateLink variable:**
+
+    ```bash
+    aws lambda get-function-configuration --function-name "<YOUR_FORWARDER>" --query 'Environment.Variables.DD_USE_PRIVATE_LINK'
+    ```
+
+3. **Review your log filtering patterns:**
+    - If using `IncludeAtMatch` or `ExcludeAtMatch`, test your patterns against log messages only
+    - Remove any JSON escaping (e.g., `\"` → `"`)
+
+#### Testing
+
+After upgrading:
+
+1. Verify logs are being forwarded to Datadog
+2. Check that filtering rules still work as expected
+3. Confirm tag enrichment is working (check logs in Datadog Explorer)
+4. Monitor forwarder execution duration and errors in CloudWatch