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

[gelanivishal]

… 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)

[sidolov]

@vgelani , port to current release line already created: #15842
I'm closing this PR as a duplicate.