[FEATURE REQUEST] Bulk delete KV Store entries by prefix / key list

[maninderpreetsingh]

Is your feature request related to a problem? Please describe.
fastly kv-store-entry delete only supports deleting a single key (--key) or deleting everything (--all). In real usage, often need to delete many keys that match a pattern (for example, everything starting with user:) or delete a known set of keys. Today that requires a script: list keys, filter them externally, then loop and delete one-by-one. This is inconvenient, slow for large key sets, and error-prone.

Describe the solution you'd like
Add a bulk delete option that supports deleting multiple keys in one command, without requiring external scripting.

Preferred options:

• Delete by prefix (consistent with kv-store-entry list --prefix):
  fastly kv-store-entry delete --store-id <id> --prefix <prefix>

• Delete by providing a list of keys directly (repeatable flag):
  fastly kv-store-entry delete --store-id <id> --key <k1> --key <k2> --key <k3>

Optional additions that would improve safety and usability:

• Confirmation prompt showing how many keys will be deleted (unless --auto-yes is set)
• --dry-run to preview which keys would be deleted
• Concurrency support for faster deletes (similar to --all)

Describe alternatives you've considered
Manual scripting: kv-store-entry list --prefix ... → filter with grep → loop kv-store-entry delete --key .... This works, but it adds extra code, is slower for large key sets, and increases the risk of deleting the wrong keys.