[CHORE] Add info about migration on issue templates

[djorkaeffalexandre]

@RocketChat/android

Closes #ISSUE_NUMBER

Changes: [Add here what changes were made in this issue and if possible provide links.]

Screenshots or GIF for the change:

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[CLAassistant]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}