feat: support setting (non-essential) vue-meta options by user

[pimlie]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

With v2.3 vue-meta will introduce more non-essential plugin options. These options can also be set runtime, but it'd be nice if they could also just be set from the nuxt.config.

Adding the options to the SPA renderer doesnt have any useful effect for the moment, except maybe for setting a custom ssrAppId (which is ill-advised). So thats mostly included to be complete and maybe future vue-meta options.

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly. (PR: #)
• I have added tests to cover my changes (if not applicable, please state why)
• All new and existing tests are passing.

[codecov-io]

Codecov Report

Merging #6432 into dev will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev    #6432   +/-   ##
=======================================
  Coverage   95.61%   95.61%           
=======================================
  Files          79       79           
  Lines        2689     2689           
  Branches      694      694           
=======================================
  Hits         2571     2571           
  Misses        101      101           
  Partials       17       17

Flag	Coverage Δ
#e2e	100% <ø> (ø)	⬆️
#fixtures	50.79% <ø> (ø)	⬆️
#unit	92.26% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
packages/config/src/config/_app.js	100% <ø> (ø)	⬆️
packages/vue-renderer/src/renderers/spa.js	87.87% <ø> (ø)	⬆️

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[Atinux]

LGTM