(you don't have to strictly follow this form)

**Describe the bug**
When using `ORDER BY column_name COLLATE 'en'`, `COLLATE` is ignored if `column_name` is the primary key
 
**How to reproduce**
* version 21.1.2
* `CREATE TABLE` statements for all tables involved:
```
CREATE TABLE test.test_collation
(
    `v` String,
    `v2` String
)
ENGINE = MergeTree
ORDER BY v
SETTINGS index_granularity = 8192
```
* Sample data:
```
insert into test.test_collation values ('A', 'A')
insert into test.test_collation values ('B', 'B')
insert into test.test_collation values ('C', 'C')
insert into test.test_collation values ('a', 'a')
insert into test.test_collation values ('b', 'b')
insert into test.test_collation values ('c', 'c')
```
* Queries to run that lead to unexpected result
Primary key
```
SELECT *
FROM test.test_collation
ORDER BY v ASC COLLATE 'en'

Query id: fa84ae7a-abe7-4886-99cd-eba7ad5d5fc4

┌─v─┬─v2─┐
│ A │ A  │
│ B │ B  │
│ C │ C  │
│ a │ a  │
│ b │ b  │
│ c │ c  │
└───┴────┘
```
Separate column
```
SELECT *
FROM test.test_collation
ORDER BY v2 ASC COLLATE 'en'

Query id: 04401f85-3cb2-442c-8c89-e3328d1615cd

┌─v─┬─v2─┐
│ a │ a  │
│ A │ A  │
│ b │ b  │
│ B │ B  │
│ c │ c  │
│ C │ C  │
└───┴────┘
```

**Expected behavior**
Both of these queries to return the rows in the same order

ColumnsWithTypeAndName columns = prewhere_actions->getResultColumns();
        auto required_columns = prewhere_actions->getRequiredColumns();
        NameSet prewhere_input_names;
        NameSet unused_source_columns;
        for (const auto & col : required_columns)
            prewhere_input_names.insert(col.name);
        for (const auto & column : sourceColumns())
        {
            if (prewhere_input_names.count(column.name) == 0)
            {
                columns.emplace_back(column.type, column.name);
                unused_source_columns.emplace(column.name);
            }
        }
        chain.steps.emplace_back(std::make_unique<ExpressionActionsChain::ExpressionActionsStep>(
                std::make_shared<ActionsDAG>(std::move(columns))));
        chain.steps.back()->additional_input = std::move(unused_source_columns);
        chain.getLastActions();
        chain.addStep();
    }
    return prewhere_actions;
}
void SelectQueryExpressionAnalyzer::appendPreliminaryFilter(ExpressionActionsChain & chain, ActionsDAGPtr actions_dag, String column_name)