Support default credential provider chain for Iceberg sink storage authentication

[disha-chhabra-0002]

Description

While configuring the Iceberg sink connector in Iggy Connectors, I noticed that the configuration currently requires explicitly providing storage credentials:

store_access_key_id = "admin"
store_secret_access_key = "password"

If these fields are not provided, the connector fails during initialization with an error such as:

Failed to parse configuration for sink connector with ID: 1.
missing field `store_access_key_id`

Logs:

ERROR connector: connector_target="iggy_connector_sdk::sink" Failed to parse configuration for sink connector with ID: 1. missing field `store_access_key_id`
ERROR iggy_connectors::sink: Plugin initialization failed (ID: 1)
ERROR iggy_connectors::sink: Failed to initialize sink container with name: Iceberg sink (iceberg)

In many production environments (e.g., AWS, Kubernetes), it is considered best practice to avoid static access keys and instead rely on the default credential provider chain, such as:

• IAM roles
• Instance profiles
• Workload identity
• Environment credentials

Suggested Improvement

Add support for using the default credential provider chain for storage authentication.

Component

Connectors

[gomnitrix]

@hubcio Hi, could I get assigned to this issue?

[hubcio]

@gomnitrix yes, go ahead.

[hubcio]

@gomnitrix how's progress? do you need any help / do you have any questions?

[gomnitrix]

@gomnitrix how's progress? do you need any help / do you have any questions?

@hubcio Hi! So sorry for the delay. I actually finished the code changes after getting assigned. It wasn't a big change, but I got stuck on the testing part: I wasn't sure if I needed to set up a full local Iceberg/S3 cluster and use real credentials just to verify the default provider end-to-end. I should have asked about this much earlier, but I got caught up with real-life stuff lately and let it slip. I'm really sorry about that!
Do you think a full local e2e test is strictly necessary for this? If not, I can open the PR and see if reviewers have any suggestions. Let me know what you think!