Consolidate security considerations for the GitLab for Jira Cloud app

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@Andysoiron

I've added the security considerations section as a starting point to collect answers to customer questions. My plan was to compile the content of the two issues mentioned above into documentation. No information was left out on purpose. Priorities changed and I didn’t get to work on this.

Maybe we can split the information up into:

CC @m_frankiewicz

Edited by 🤖 GitLab Bot 🤖