feat: Add new config option for deduplicating import declarations

[AdrianGonz97]

Closes #298

Adds a new config option, importOrderMergeImports (the name could be better), that deduplicates import declarations from the same source.

For example, provided the following code:

import * as NamespacedImport from './example';
import DefaultImport from './example';
import { NamedImport1 } from './example';
import { NamedImport2 } from './example';
import { NamedImport3 } from './example';

will be formatted into:

// namespaced imports are ignored as they cannot contain other specifier types
import * as NamespacedImport from './example'; 
import DefaultImport, { NamedImport1, NamedImport2, NamedImport3 } from './example';

As for the name, some alternatives I've considered could be importOrderDeduplicateImports or importOrderCombineImportSpecifiers. Suggestions are welcomed!