[receiver/haproxy] Enable re-aggregation feature (#46518)

## Summary
- Enable dynamic metric reaggregation in the HAProxy receiver
- Set `reaggregation_enabled: true` in `metadata.yaml`
- Add `requirement_level: recommended` to the `status_code` attribute

Fixes #46357
Part of #45396

## Test plan
- [x] `go generate ./...` ran successfully
- [x] `make gci` ran successfully
- [x] `make generate-schemas` ran successfully
- [x] `go test ./...` passes
- [x] `make chlog-validate` passes

Signed-off-by: Nick Nikolakakis <nonicked@protonmail.com>

Author: nicknikolakakis

.chloggen/46357-haproxy-enable-reaggregation.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: 'enhancement'
+
+# The name of the component, or a single word describing the area of concern, (e.g. receiver/filelog)
+component: receiver/haproxy
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Enable dynamic metric reaggregation in the HAProxy receiver.
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [46357]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

receiver/haproxyreceiver/internal/metadata/config.schema.yaml

@@ -1,11 +1,23 @@
 $defs:
+  attribute_config:
+    description: AttributeConfig holds configuration information for a particular metric.
+    type: object
+    properties:
+      enabled:
+        type: boolean
   attribute_status_code:
     description: AttributeStatusCode specifies the value status_code attribute.
     type: integer
   metric_config:
     description: MetricConfig provides common config for a particular metric.
     type: object
     properties:
+      aggregation_strategy:
+        type: string
+      attributes:
+        type: array
+        items:
+          type: string
       enabled:
         type: boolean
   metrics_builder_config: