RANGER-5406 Support export policies in a segmented manner

[yunyezhang-work]

What changes were proposed in this pull request?

In big data production environments, customers create a massive number of policies, often reaching hundreds of thousands or even millions. Exporting the entire set of policies for disaster recovery would result in an enormous data volume and extremely slow import speeds into the backup cluster. Our current experimental data shows that importing 10,000 policies via the API is very memory-intensive and takes approximately 15 minutes. Importing 100,000 policies via the API will take 2.5h or even longer.

With an even larger number of policies, memory consumption will increase significantly, and insufficient memory can cause import interruptions. Therefore, we recommend modifying the API to allow for segmented export. This will save memory and ensure data reliability when importing to other clusters for disaster recovery.

How was this patch tested?

To manually test this feature, you can send an HTTP request to the ranger. Using a shell command as an example:

Without the segmentation parameter, calling the export API getPoliciesInJson will export all policies. As shown in the figure, there are 18 policies in this environment for hdfs-xxx.
curl -u$USER:$PASSWORD -XGET "http://$RANGER_HOST:$RANGER_PORT/service/plugins/policies/exportJson?serviceName=$SERVICE&checkPoliciesExists=true" -v -o export.json

Adding the segmentation parameter will export the policies for the specified start and end position range. As shown in the figure, policies 1-5 of hdfs-xxx are exported.
curl -u$USER:$PASSWORD -XGET "http://$RANGER_HOST:$RANGER_PORT/service/plugins/policies/exportJson?serviceName=$SERVICE&checkPoliciesExists=true&beginIndex=$BEGIN_INDEX&offsetIndex=$OFFSET_INDEX" -v -o export_${BEGIN_INDEX}_${OFFSET_INDEX}.json

[vyommani]

The latest changes look good to me. Since I'm not the official reviewer, you'll need approval from at least one Apache reviewer.

[yunyezhang-work]

@kumaab @mneethiraj Please review this PR regarding feature optimization for the export interface.