(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

const auto * ast = child->as<ASTOrderByElement>();
        if (!ast || ast->children.empty())
            throw Exception("Bad order expression AST", ErrorCodes::UNKNOWN_TYPE_OF_AST_NODE);
        ASTPtr order_expression = ast->children.at(0);
        step.addRequiredOutput(order_expression->getColumnName());
        if (ast->with_fill)
            with_fill = true;
    }
    if (optimize_read_in_order)
    {
        for (auto & child : select_query->orderBy()->children)
        {
            auto actions_dag = std::make_shared<ActionsDAG>(columns_after_join);
            getRootActions(child, only_types, actions_dag);
            order_by_elements_actions.emplace_back(
                std::make_shared<ExpressionActions>(actions_dag, ExpressionActionsSettings::fromContext(getContext())));
        }
    }
    NameSet non_constant_inputs;
    if (with_fill)
    {
        for (const auto & column : step.getResultColumns())
            if (!order_by_keys.count(column.name))
                non_constant_inputs.insert(column.name);
    }
    auto actions = chain.getLastActions();
    chain.addStep(non_constant_inputs);
    return actions;
}
bool SelectQueryExpressionAnalyzer::appendLimitBy(ExpressionActionsChain & chain, bool only_types)