ebs br: add tag TiDBCluster-BR to snapshots

[BornChanger]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

Run EBS snapshot backup

2. What did you expect to see? (Required)

Snapshot generated has tag with key TiDBCluster-BR

3. What did you see instead (Required)

The tag is missing

4. What is your TiDB version? (Required)

[BornChanger]

/component br

[BornChanger]

/label affects-6.5

[BornChanger]

/label affects-7.1

[BornChanger]

/label affects-7.5

[BornChanger]

/severity major

[BornChanger]

/remove-label may-affects-5.4