Add an :if_not_exists option to create_table

[fatkodima]

This PR updates (it has no activity nearly for 2 years) this #16376 according to master.
r? @maclover7 @arthurnn

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[fatkodima]

Just noticed, whole line should be replaced with force for create_table and same in the next test

[rafaelfranca]

👍

[rafaelfranca]

👍

[fatkodima]

@rafaelfranca Is there any chance to get also this into 5.2?

[fatkodima]

@pixeltrix Updated this pr.
@sebcioz Kudos for pushing this forward!

Requested changes have been made

[pixeltrix]

@fatkodima thanks! 👍

[pedrofurtado]

@pixeltrix @rafaelfranca It's great to include this in Rails docs 👍

[shootingfly]

Unbelievable! When you create table, you will drop table! Why keep if_exists default to true?
When I migrate from 5.2 to 6.0, this MR drop all tables in stage environment.

[pixeltrix]

@shootingfly I'm unsure what you mean by your comment and I noticed your 👎🏻 on this comment - that reference to drop_table is in a Rails test and not in code that will get executed in an application. Are you saying that you saw all your tables dropped when upgrading from Rails 5.2 to 6.0? If so please open a new issue describing the problem, thanks.