Add upgrade handler for v8

[ValarDragon]

What is the purpose of the change

This PR adds boilerplate for the v8 upgrade handler. Simplifies the logic for upgrade store handler updates. Intended as a precursor for #1301

Brief change log

• Adds boilerplate for the v8 upgrade handler. I don't think this necessitates an entry in the actual changelog.

Testing and Verifying

This change should be tested in upcoming upgrade handler testing on testnets / in framework. It needs an end to end test to properly test changes to the store loaders.

Documentation and Release Note

• Does this pull request introduce a new feature or user-facing behavior changes? no
• Is a relevant changelog entry added to the Unreleased section in CHANGELOG.md? no
• How is the feature or change documented? NA

[codecov-commenter]

Codecov Report

Merging #1304 (535240d) into main (0cfa729) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1304   +/-   ##
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  Coverage   20.26%   20.26%           
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  Files         203      203           
  Lines       26824    26824           
=======================================
  Hits         5437     5437           
  Misses      20377    20377           
  Partials     1010     1010           

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[mattverse]

LGTM! I was wondering if there's any logic we need to handle within the upgrade handler for v8.

Should we also create an issue to change main to v8?

[alexanderbez]

Template LGTM!