text: Title: Table prefixes are not picked up by autogenerate
  Body: **Describe the bug**
  Currently sqlalchemy [`Table.prefixes`](https://docs.sqlalchemy.org/en/13/core/metadata.html#sqlalchemy.schema.Table.params.prefixes) are not picked up by alembic when generating a migration using 
  `alembic revision --autogenerate`
  **Expected behavior**
  The `prefixes` are picked up by alembic. I've not tested it with other table keyboard, but maybe it's a more common theme.
  
  **To Reproduce**
  Please try to provide a [Minimal, Complete, and Verifiable](http://stackoverflow.com/help/mcve) example, with the migration script and/or the SQLAlchemy tables or models involved.
  See also [Reporting Bugs](https://www.sqlalchemy.org/participate.html#bugs) on the website.
  
  ```py
  # Add a new table like this one to the metadata
  import sqlalchemy as sa
  
  sa.Table(
      "foo",
      metadata,
      sa.Column("id", sa.Integer(), primary_key=True),
      sa.Column("other", sa.Integer),
      prefixes=["UNLOGGED"],
  )
  
  ```
  
  **Error**
  
  ```
  # The reflected migration code generated is
  def upgrade():
      # ### commands auto generated by Alembic - please adjust! ###
      op.create_table(
          "foo",
          sa.Column("id", sa.Integer(), nullable=False),
          sa.Column("other", sa.Integer(), nullable=True),
          sa.PrimaryKeyConstraint("id"),
      )
      # ### end Alembic commands ###
  ```
  
  **Versions.**
   - OS: windows
   - Python: 3.7.7
   - Alembic: 1.4.2
   - SQLAlchemy: 1.3.18
   - Database: postgres
   - DBAPI: pycopg2
  
  **Additional context**
  Manually adding `prefixes=[...]` to the `create_table` function after autogenerate does work correctly, so this is just a nice to have feature
  
  **Have a nice day!**
  