feat: Add dataplex-get-data-asset tool

[theantagonist9509]

Important

Stacked Changeset: This PR depends on changes in previous PRs (#3337, #3499, #3500).

• Please merge previous PRs first before reviewing/merging this one.
• The file diff below will appear large as it includes its ancestors' commits. It will resolve itself once the preceding PRs are merged and this branch is synced.

This PR implements the dataplex-get-data-asset tool for the Dataplex
(Knowledge Catalog) source, allowing users to fetch detailed configuration
metadata for a single Data Asset.

Changes overview:

• Dataplex Source: Implemented GetDataAsset to retrieve details for a
  specific asset by location, data product, and asset ID. The response maps the
  resource URI, labels, and access group configurations.
• New Tool: Created the dataplex-get-data-asset tool exposing locationId ,
  dataProductId , and dataAssetId parameters.
• Tests:
  • Added unit tests for tool configuration parsing.
  • Added integration tests asserting successful metadata retrieval and
    authorization checks.
• Documentation: Created the reference page for the tool, updated the
  Dataplex source guide, and added it to the main capabilities list.

[gemini-code-assist]

Code Review

This pull request adds support for Dataplex Data Products and Data Assets by introducing four new tools: dataplex-list-data-products, dataplex-get-data-product, dataplex-list-data-assets, and dataplex-get-data-asset. It includes the necessary client initializations, source methods, unit and integration tests, prebuilt configurations, and documentation. A critical issue was found in internal/sources/dataplex/dataplex.go where the error check for GetOperation was accidentally removed, which could lead to a nil pointer panic during protojson marshalling if the operation retrieval fails.