docs: add upgrading guide for v8

[matthewmayer]

fix #1518

[codecov]

Codecov Report

Merging #1517 (b706fce) into next (a338bb2) will not change coverage.
The diff coverage is n/a.

❗ Current head b706fce differs from pull request most recent head 02f09e4. Consider uploading reports for the commit 02f09e4 to get more accurate results

Additional details and impacted files

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##             next    #1517   +/-   ##
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  Coverage   99.63%   99.63%           
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  Files        2216     2216           
  Lines      238845   238845           
  Branches     1029     1029           
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  Hits       237983   237983           
  Misses        841      841           
  Partials       21       21           

[ST-DDT]

Could you please escape the faker method references/wrap them in code blocks? Some of the references are treated as links:

Also the link in the sidebar has the wrong title:

[matthewmayer]

Could you please escape the faker method references/wrap them in code blocks? Some of the references are treated as links:

Also the link in the sidebar has the wrong title:

done