Cherry-pick #23546 to 7.x: Remove dimension TAGS from aws metricbeat module documentation for billing

[kaiyan-sheng]

Cherry-pick of PR #23546 to 7.x branch. Original message:

https://github.com/elastic/beats/blob/7.11/x-pack/metricbeat/module/aws/billing/billing.go#L34-L42 :

	// This list is from https://github.com/aws/aws-sdk-go-v2/blob/master/service/costexplorer/api_enums.go#L60-L90
	supportedDimensionKeys = []string{
		"AZ", "INSTANCE_TYPE", "LINKED_ACCOUNT", "OPERATION", "PURCHASE_TYPE",
		"REGION", "SERVICE", "USAGE_TYPE", "USAGE_TYPE_GROUP", "RECORD_TYPE",
		"OPERATING_SYSTEM", "TENANCY", "SCOPE", "PLATFORM", "SUBSCRIPTION_ID",
		"LEGAL_ENTITY_NAME", "DEPLOYMENT_OPTION", "DATABASE_ENGINE",
		"CACHE_ENGINE", "INSTANCE_TYPE_FAMILY", "BILLING_ENTITY",
		"RESERVATION_ID",
	}

https://github.com/elastic/beats/blob/master/x-pack/metricbeat/module/aws/billing/_meta/docs.asciidoc mentions TAGS :

group_by_dimension_keys: A list of keys used in Cost Explorer to group by dimensions. Valid values are AZ, INSTANCE_TYPE, LEGAL_ENTITY_NAME, LINKED_ACCOUNT, OPERATION, PLATFORM, PURCHASE_TYPE, SERVICE, TAGS, TENANCY, and USAGE_TYPE.

https://github.com/aws/aws-sdk-go-v2/blob/main/service/costexplorer/types/enums.go#L171-L203 :

func (Dimension) Values() []Dimension {
	return []Dimension{
		"AZ",
		"INSTANCE_TYPE",
		"LINKED_ACCOUNT",
		"LINKED_ACCOUNT_NAME",
		"OPERATION",
		"PURCHASE_TYPE",
		"REGION",
		"SERVICE",
		"SERVICE_CODE",
		"USAGE_TYPE",
		"USAGE_TYPE_GROUP",
		"RECORD_TYPE",
		"OPERATING_SYSTEM",
		"TENANCY",
		"SCOPE",
		"PLATFORM",
		"SUBSCRIPTION_ID",
		"LEGAL_ENTITY_NAME",
		"DEPLOYMENT_OPTION",
		"DATABASE_ENGINE",
		"CACHE_ENGINE",
		"INSTANCE_TYPE_FAMILY",
		"BILLING_ENTITY",
		"RESERVATION_ID",
		"RESOURCE_ID",
		"RIGHTSIZING_TYPE",
		"SAVINGS_PLANS_TYPE",
		"SAVINGS_PLAN_ARN",
		"PAYMENT_OPTION",
	}
}

I think we just need to remove TAGS from the documentation, when used metricbeat won't start with this error

ERROR  instance/beat.go:956  Exiting: 1 error: error unpack raw module config using UnpackConfig: costexplorer GetCostAndUsageRequest does not support dimension key: TAGS accessing '0.cost_explorer_config' (source:'/usr/share/metricbeat/modules.d/aws.yml')

[elasticmachine]

Pinging @elastic/integrations (Team:Platforms)