Flutter: Building and distributing a .ipa File without Mac/Apple Developer Account?

Question

I'm new to Flutter and Travis CI, so im having minor problems setting up the following. From what i read, it should be possible, but im not sure how exactly.

My current setup uses my existing Travis CI account, to build all my changes using flutter build ios --no-codesign . This generally works and should output a Runner.app -File. My aim now is, to transform this File into a usable .ipa, which i can distriute to my personal iPhone/iPad via www.diawi.com.

I know that it is generally possible, to make Travis CI to commit results back to github, and i also know, that it should be possible, to build/create an .ipa from the .app file using the CLI of XCode.

Can someone help/hint me with building a full build.sh , which performs the flutter build, the xcode build, the ipa-extraction and the push of the .ipa to git?