Index Shard Stores API not representable in the spec

The `indices.shard_stores` response isn't representable due to the random shard name being a key in a dictionary containing other known fields (in the below example `sPa3OgxLSYGvQ4oPs-Tajw`):

```json
{
"indices": {
"my-index-00001": {
"shards": {
"0": {
"stores": [
{
"sPa3OgxLSYGvQ4oPs-Tajw": {
"name": "node_t0",
"ephemeral_id": "9NlXRFGCT1m8tkvYCMK-8A",
"transport_address": "local[1]",
"attributes": {},
"roles": []
},
"allocation_id": "2iNySv_OQVePRX-yaRH_lQ",
"allocation": "primary",
"store_exception": "..."
}
]
}
}
}
}
}
```

Start by locating the specification entry for the indices.shard_stores response and compare its model with the JSON example. Check how the dynamic shard-name key must coexist with the known fields, then run the existing specification validation checks. Done means this response is representable without losing any fields.

Written by the indexing model from the issue text.