[mdatagen] Fix invalid test code generation for conditionally_required enum attributes

When an attribute has requirement_level: conditionally_required and an enum
type, the generated metrics_test.go was passing the enum constant directly
(an integer) to With{Attr}MetricAttribute(), which expects a string. This
caused compile errors in generated test code.

Fix by introducing a getConditionalAttributeValue template helper that
appends .String() to enum attribute constants, producing the correct string
type. Also fix config.go.tmpl to only import "slices" when there are
actually required attributes in reaggregation metrics, avoiding unused
import compile errors.

Add assertions for conditionally_required attributes in the reaggregation
branch of metrics_test.go.tmpl so the generated tests verify their presence
and value, matching the pattern used in the non-reaggregation branch.

Add TestDeprecatedRecordMethods to exercise the deprecated
MetricsBuilder.Record*DataPoint wrapper methods that exist for backward
compatibility when metrics have entities. The existing test only exercised
the entity builder path, leaving lines in generated_metrics.go uncovered
and failing the Codecov patch coverage gate.

Restore stdlib/third-party/local import group separation in generated
files to satisfy impi linter rules.

Regenerate sampleconnector and sampleentityreceiver fixtures.

Resolves #14196

Signed-off-by: Kc Balusu <kcbalusu@meta.com>

Author: Krishnachaitanyakc

cmd/mdatagen/internal/sampleconnector/documentation.md

@@ -28,7 +28,7 @@ The metric will be become optional soon.
 | ---- | ----------- | ------ | ----------------- | ------------------- |
 | string_attr | Attribute with any string value. | Any Str | Recommended | - |
 | state | Integer attribute with overridden name. | Any Int | Recommended | - |
-| enum_attr | Attribute with a known set of string values. | Str: ``red``, ``green``, ``blue`` | Recommended | - |
+| enum_attr | Attribute with a known set of string values. | Str: ``red``, ``green``, ``blue`` | Conditionally Required | - |
 | slice_attr | Attribute with a slice value. | Any Slice | Recommended | - |
 | map_attr | Attribute with a map value. | Any Map | Recommended | - |
 
@@ -58,7 +58,7 @@ Monotonic cumulative sum int metric with string input_type enabled by default.
 | ---- | ----------- | ------ | ----------------- | ------------------- |
 | string_attr | Attribute with any string value. | Any Str | Recommended | - |
 | state | Integer attribute with overridden name. | Any Int | Recommended | - |
-| enum_attr | Attribute with a known set of string values. | Str: ``red``, ``green``, ``blue`` | Recommended | - |
+| enum_attr | Attribute with a known set of string values. | Str: ``red``, ``green``, ``blue`` | Conditionally Required | - |
 | slice_attr | Attribute with a slice value. | Any Slice | Recommended | - |
 | map_attr | Attribute with a map value. | Any Map | Recommended | - |
 

cmd/mdatagen/internal/sampleconnector/internal/metadata/generated_entity_metrics.go

@@ -93,6 +93,7 @@ attributes:
     description: Attribute with a known set of string values.
     type: string
     enum: [red, green, blue]
+    requirement_level: conditionally_required
 
   map_attr:
     description: Attribute with a map value.