add inline_reference parameter

add inline_reference parameter

Added ``inline_references`` parameter to :meth:`.Operations.add_column`
which allows rendering of ``REFERENCES`` clauses inline within the ``ADD
COLUMN`` directive rather than as a separate ``ADD CONSTRAINT`` directive.
This syntax is supported by PostgreSQL, Oracle, MySQL 5.7+, and MariaDB
10.5+, and can provide performance benefits on large tables by avoiding
full table validation when adding a nullable foreign key column.

Fixes: #1780
Change-Id: I6749c0a2b92af61e95decea552c8afdd93e11c19