Add i18n support

[silvester-pari]

https://vue-i18n.intlify.dev/guide/essentials/started.html

This would allow us to offer a translated/multi-language version of git-clerk.
We could let the config be overridden via the gitClerkConfig, e.g.

globalThis.gitClerkConfig = {
  i18n: {
    locale: 'ja',
    fallbackLocale: 'en',
    messages: {
      en: {
        message: {
          hello: 'hello world'
        }
      },
      ja: {
        message: {
          hello: 'こんにちは、世界'
        }
      }
    }
  }
}

This config would then be deepmerged with the default config, allowing to only override certain messages.