Add support for INDEX INCLUDE

[aidanharan]

Add support for index include as requested in #473

Running the following:

connection.add_index("testings", "last_name", include: :foo)

Before this PR generates:

CREATE INDEX [index_testings_on_last_name] ON [testings] ([last_name])

After the PR it will generate:

CREATE INDEX [index_testings_on_last_name] ON [testings] ([last_name]) INCLUDE ([foo])

Multiple include columns are supported using:

connection.add_index("testings", "last_name", include: [:foo, :bar])

Ref: rails/rails#44803

[aidanharan]

Tests will be included as part of the ActiveRecord tests after rails/rails#54532 is merged.