Remove unneeded fields in cloud provider credential structs

[renormalize]

How to categorize this issue?

/area backup
/kind cleanup

What would you like to be added:

As can be seen in the following structs, the bucketName field is exposed by the cloud provider credential structs, which the secrets' data is unmarshalled into.

etcd-backup-restore/pkg/snapstore/s3_snapstore.go

Lines 50 to 65 in 81c4c17

	type awsCredentials struct {
	SSECustomerAlgorithm *string `json:"sseCustomerAlgorithm,omitempty"`
	SSECustomerKey *string `json:"sseCustomerKey,omitempty"`
	Endpoint *string `json:"endpoint,omitempty"`
	S3ForcePathStyle *bool `json:"s3ForcePathStyle,omitempty"`
	InsecureSkipVerify *bool `json:"insecureSkipVerify,omitempty"`
	TrustedCaCert *string `json:"trustedCaCert,omitempty"`
	RequestChecksumCalculation *string `json:"requestChecksumCalculation,omitempty"`
	ResponseChecksumValidation *string `json:"responseChecksumValidation,omitempty"`
	AccessKeyID string `json:"accessKeyID"`
	Region string `json:"region"`
	SecretAccessKey string `json:"secretAccessKey"`
	BucketName string `json:"bucketName"`
	RoleARN string `json:"roleARN"`
	TokenPath string `json:"tokenPath"`
	}

etcd-backup-restore/pkg/snapstore/abs_snapstore.go

Lines 93 to 99 in 81c4c17

	type absCredentials struct {
	Domain *string `json:"domain,omitempty"`
	BucketName string `json:"bucketName"`
	StorageAccount string `json:"storageAccount"`
	StorageKey string `json:"storageKey"`
	EmulatorEnabled bool `json:"emulatorEnabled,omitempty"`
	}

etcd-backup-restore/pkg/snapstore/swift_snapstore.go

Lines 63 to 72 in 81c4c17

	type swiftCredentials struct {
	AuthType string `json:"authType"`
	AuthURL string `json:"authURL"`
	BucketName string `json:"bucketName"`
	DomainName string `json:"domainName"`
	Region string `json:"region"`
	TenantName string `json:"tenantName"`
	passwordCredential
	applicationCredential
	}

However, this field is never actually used in any of the code, in any of the providers. The bucket name is provided as a flag, and is passed to all relevant places from there.

These fields should be removed, so that all extensions that create the etcd-backup secrets don't have to populate this field anymore.

Why is this needed:

We should remove unneeded fields and cleanup the public interfaces we have with consumers, like the secret created for cloud provider credentials.

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