Manually recreate a table if any column needs to add/remove constraint

[elefeint]

DuckDB does not yet support ALTER TABLE with any constraints modifications (even DROP COLUMN fails if the column has a primary key).

This PR works around the limitation by renaming the original table, creating a new table with the correct structure, and copying all the old data from columns that were present in both the old table and the new table structure into it.

Fixes #44.
Fixes #2 in a better way (by making it work rather than throwing exception).
Fixes ECO-149

[hrl20]

should this be false initially?

[elefeint]

no, it was "false" in create-table block above. This is turning an existing column that was previously NOT a primary key into a primary key.

[hrl20]

the test block below // Alter Table to make an existing (unique valued) column into a primary key
has the comment // turn existing column into a primary key

    auto col2 = request.mutable_table()->add_columns();
    col2->set_name("name");
    col2->set_type(::fivetran_sdk::DataType::STRING);
    col2->set_primary_key(true); // turn existing column into a primary key

so i thought this block should not set this column to a primary key.

[elefeint]

huh, you are right; I think I duplicated something somewhere

[elefeint]

I switched it back to false, and refactored to make it a bit easier to read

[hrl20]

why can a change of type happen in place?

[hrl20]

or rather, why does this check come before the new_col_it->second.primary_key != col.primary_key check, and take precedence over change of primary key status

[elefeint]

if the types are compatible, it will work. If they are not, this should not be happening in the first place, and recreating a table won't really help

D create table a (col short);
D insert into a (col) values (1), (2), (3);
D select * from a;
┌───────┐
│  col  │
│ int16 │
├───────┤
│     1 │
│     2 │
│     3 │
└───────┘
D alter table a alter col type INT;
D select * from a;
┌───────┐
│  col  │
│ int32 │
├───────┤
│     1 │
│     2 │
│     3 │
└───────┘

[elefeint]

oh, that's a good point; I'll switch them

[elefeint]

done!