feat(a11y): add access keys shortcuts

[userquin]

This PR includes:

• link for skip navigation in layout: SkipContent.ts component (cannot use anchor in vue SFC, NuxtLink doesn't support hash only) => check if we can get the full path and use it in the skip content link (using hash, nuxt is navigating, the aria announcer changes)
• link for jump to content anchor to be included in all pages via skip-content attribute in MainContent SFC: SkipContentLink.vue SFC
• access keys module in constants to define them: key + access key
• new i18n json entry: a11y.skip_navigation
• add accesskey to aside (WIP)
• include accesskeys in shortcuts and maybe include a page (I need to review a11y in the dialog) (WIP)

NOTE: to activate accesskeys you need to check your browser documentation, on my Windows laptop and using Chrome I can activate Skip navigation using Alt + 1. Once Alt + 1 pressed you can press Tab, should focus the next focusable element in the main content of the page, rn only settings pages with Skip navigation links included.

EDIT: I need to change the styles in SkipContent.ts and SkipCintentLink.vue, there is layout shift when activating the link and getting the focus the link in SkipContentLink.vue , @patak-dev maybe you can check it, I have a lot of work changing all pages.

/cc @danielroe @antfu for nuxt-a11y https://www.nomisweb.co.uk/home/accesskeys.asp#content-anchor

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