to have a complete guide about CI/CD I think is not possible.. there is too much about processes, tools and customizations. Also the changes are fast and it should be updated every month.
The short answer is:
I have recently performed a complete CI/CD process in an enterprise environment using some of what you just told:
devs pushing on gitlab (java, react) ...
You will add flyway migration as it is, nothing special and than this migration will be applied before the application is opened for service.
There is no specific difference between versions as far as flyway migrations concerns.
If they are master slave than migration can be applied on master instances only.