Add v5 migration notes

[nscuro]

Description

Adds v5 migration notes.

Addressed Issue

Relates to #6105

Additional Details

N/A

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have added corresponding update logic
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[owasp-dt-bot]

✅ Snyk checks have passed. No issues have been found so far.

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✅	Open Source Security	0	0	0	0	0 issues

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[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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