Add special case - mdb_admin group

[Alena0704]

Allow mdb_admin role to manage resource groups

Summary

Backport of open-gpdb commit 3ac99962ad ("Add special case - mdb_admin group")
by Andrey Borodin, which extends the resource-group permission checks so a
non-superuser member of the mdb_admin role can CREATE / ALTER / DROP
resource groups and call pg_resgroup_move_query().

Without this patch, a managed-cluster user that holds CREATEROLE / CREATEDB
but not SUPERUSER (the typical "MDB admin" persona) hits:

ERROR: must be superuser to create resource groups

even though they own the cluster from the operator's point of view.

Fixes #ISSUE_Number

What does this PR do?

Type of Change

• Bug fix (non-breaking change)
• New feature (non-breaking change)
• Breaking change (fix or feature with breaking changes)
• Documentation update

Breaking Changes

Test Plan

• Unit tests added/updated
• Integration tests added/updated
• Passed make installcheck
• Passed make -C src/test installcheck-cbdb-parallel

Impact

Performance:

User-facing changes:

Dependencies:

Checklist

• Followed contribution guide
• Added/updated documentation
• Reviewed code for security implications
• Requested review from cloudberry committers

Additional Context

CI Skip Instructions

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