Add a resource for Integrations

[mathislucka]

Consult REPO.md for general instructions on the task.

We want a resource for integrations (the API is named model_registry_tokens but we don't want to use that name).

We want:

list integrations:
curl --request GET
--url https://api.cloud.deepset.ai/api/v1/model_registry_tokens
--header 'accept: application/json'

[
{
"invalid": true,
"model_registry_token_id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
"provider": "aws-bedrock",
"provider_domain": "string"
}
]

get integration:

curl --request GET
--url https://api.cloud.deepset.ai/api/v1/model_registry_tokens/provider
--header 'accept: application/json'

Provider needs to be one of:
aws-bedrock
azure-document-intelligence
azure-openai
cohere
deepl
google
huggingface
nvidia
openai
searchapi
snowflake
unstructured
voyage-ai
wandb-ai
mongodb
together-ai

{
"invalid": true,
"model_registry_token_id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
"provider": "aws-bedrock",
"provider_domain": "string"
}

Add the resource with the two methods, add appropriate models, add unit and integration tests.