[Feature Request] el-table type selection with slot header and template custom

### Existing Component
Yes

### Component Name
el-table

### Description


check



{{ scope.row.ok }}

i need el-table-column with type selection
but in value i need custom or showing the checkbox with data value row.ok and change header of checkbox to string.
then i have 3 column where the column have checkbox and string with different data
how to trigger the all checkbox are checked in column1, column2 and column3 ?

before
------------------
- [x] // {checkbox}

|{checkbox}|
| ------|
|{checkbox}|
|{checkbox}|

after
------------------
- [x] // {checkbox}

|string label|
| ------|
|{checkbox} string value ok|
|{checkbox} string value ok|

the data looks like
```
data() {
return {
tableData: {
ok: 'john' ....
ok: 'doe'.....
```
------------------