I think both are correct, or at least idiomatic, in spoken English. In British English "all I've got to say" is very common. The first answer for this stack exchange question quotes Cambridge Grammar as saying it is less common in the US: https://english.stackexchange.com/questions/120721/have-vs-have-got-in-american-and-british-english BBC English guide agrees that they're the same thing: https://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv323.shtml#:~:text=When%20we%20are%20talking%20about,are%20used%20as%20present%20tenses. I think it's less common to write "I've got to" and quite rare to see/hear it without the contraction "I have got to say".

The correct phrase is actually - "That is all I have to say".

The correct phrase is "That's all I've got to say". It's used when someone, or yourself, has no more to say in a conversation. Depending on the tone, it can be informal, even quite rude almost. I would suggest you avoid it in formal speech!

It is slang for, 'that is all I have to say'.