Strengthen index template data source acceptance coverage for alias, template JSON, and metadata/version updates

[Copilot]

Fixes #2015

elasticstack_elasticsearch_index_template data source acceptance coverage was missing validation for alias routing, never asserted alias filter, and relied on set-only checks for mappings, settings, and metadata. This change upgrades those weak assertions and adds value-change coverage for mappings, settings, metadata, and version.

• Alias coverage

  • Extend TestAccIndexTemplateDataSourceTemplate to configure and assert:
    • routing
    • normalized filter
    • existing alias fields in the same nested set assertion

• Exact JSON assertions for template fields

  • Replace set-only checks on:
    • template.0.mappings
    • template.0.settings
  • Assert compact normalized JSON values instead
  • Add a second step with changed mappings/settings to cover value updates

• Metadata/version value diversity

  • Expand TestAccIndexTemplateDataSourceMetadataVersionID into a two-step test
  • Assert exact normalized metadata JSON in both steps
  • Verify version changes from the initial value to a different updated value

• Fixture changes

  • Parameterize the template config helper so the same test can exercise multiple mappings/settings payloads without duplicating fixture structure

Example of the strengthened assertions:

resource.TestCheckTypeSetElemNestedAttrs(
	"data.elasticstack_elasticsearch_index_template.test",
	"template.0.alias.*",
	map[string]string{
		"name":           "my_alias",
		"filter":         `{"term":{"status":"active"}}`,
		"index_routing":  "shard_1",
		"routing":        "shard_1",
		"search_routing": "shard_1",
		"is_hidden":      "false",
		"is_write_index": "true",
	},
)

resource.TestCheckResourceAttr(
	"data.elasticstack_elasticsearch_index_template.test",
	"template.0.mappings",
	`{"properties":{"log_level":{"type":"keyword"}}}`,
)

---

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Note

Update whitespace formatting in acceptance tests for elasticstack_elasticsearch_index_template

Adjusts blank lines in the acceptance test files for elasticstack_elasticsearch_index_template. No functional or behavioral changes are introduced.

^{Macroscope summarized 4eeef8b. (Automatic summaries will resume when PR exits draft mode or review begins).}

[github-actions]

⚠️ Terraform acceptance tests failed for snapshot stack version 9.4.0-SNAPSHOT.
This failure is non-blocking because snapshot builds are allowed to fail.

Run: https://github.com/elastic/terraform-provider-elasticstack/actions/runs/23523647468