Add missing table aliases to fields mapping for Customer Group filter…

[maksymhopei]

… and sorting processor #15822

Description

This PR is a fix for #15822. Issue is caused by missing table alias prefixes in field mappings for customer group filter and sorting processors.

Fixed Issues

1. SQL Error: ambiguous column 'customer_group_id' in 'All customers' page in admin when extension attribute table is joined #15822: SQL Error: ambiguous column 'customer_group_id' in 'All customers' page in admin when extension attribute table is joined

Manual testing scenarios

Follow the steps described in the relevant issue.

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-cicd2]

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[magento-engcom-team]

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[magento-engcom-team]

Hi @radio. Thank you for your contribution.
Changes from your Pull Request will be available with the upcoming 2.2.6 release.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.