Follow up for #13228.
This commit adds support for a secondary storage account:
```yml
cloud:
azure:
storage:
my_account1:
account: your_azure_storage_account1
key: your_azure_storage_key1
default: true
my_account2:
account: your_azure_storage_account2
key: your_azure_storage_key2
```
When creating a repository, you can choose which azure account you want to use for it:
```sh
curl -XPUT localhost:9200/_snapshot/my_backup1?pretty -d '{
"type": "azure"
}'
curl -XPUT localhost:9200/_snapshot/my_backup2?pretty -d '{
"type": "azure",
"settings": {
"account" : "my_account2",
"location_mode": "secondary_only"
}
}'
```
`location_mode` supports `primary_only` or `secondary_only`. Defaults to `primary_only`. Note that if you set it
to `secondary_only`, it will force `read_only` to true.
79a4d9ce36