bug(replays): Use all bytes after the first newline split as the body value

[cmanallen]

closes: https://github.com/getsentry/replay-backend/issues/227

#skip-changelog

[olksdr]

I left few suggestions.
My questions is just why don't use the bytes slice directly and avoid wrapping it in the cursor and introducing another Vec, where we again just copying data.

I've tested the proposed changes locally and looks like all the tests are still passing.

Please, have a look and let me know what you think.

[cmanallen]

My questions is just why don't use the bytes slice directly and avoid wrapping it in the cursor and introducing another Vec, where we again just copying data.

@olksdr The answer to these questions and more is that I do not know rust :D. Strict code reviews are appreciated and encouraged.