feat: add new option for bulk gets for kv

[teresalves]

Creating a new part in the binding for new bulk gets, along with tests for regular gets and the bulk gets
We consider we have a POST endpoint in SGW and we send the keys in a json format as such:

{
   "keys": ["key1", "key2"]
}

However, we decided that the binding here will only be a passthrough and everything will processed in the endpoint. On top of that, since everything is processed in the binding and comes as a single response, we don't need extra logic to process metadata, we just need to make sure that the binding responds what we what. Because of these two things, we added two more parameters in the request body:

{
   "keys": ["key1", "key2"],
   "type": "text",
   "withMetadata": true
}

We added tests for:
Regular gets:

• 400s
• 500s
• 200s with text, json, stream and arrayBuffer

Bulk Gets:

• 500s
• 200s with text and json, as these will be the only supported types for now.

Note that we do not test for 400s because we will not have them. If none of the keys exist, we return a 200 but with empty values. Example:

{
   "key1": null,
   "key2": null,
 }

Original PR: #3628

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[teresalves]

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[teresalves]

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