added the list of IS connectors to documentation

[himeshsiriwardana]

Purpose

$subject

Related issue: wso2/product-is#21552

[aaujayasena]

Following the discussion with @himeshsiriwardana and @nilasini , we decided to introduce a dedicated documentation page in the official WSO2 IS documentation to list supported (tested) connectors.

Key decisions from the meeting:

• A separate documentation page will be created specifically to list the supported connectors.
• Each listed connector will include a brief description and a link to the Connector Store.
• Since the list of supported connectors may grow over time, only short descriptions will be included for maintainability.
• The document will be kept up to date whenever new connectors are tested and verified for support.