Updating app template to use compatible icon

[tolzhabayev]

What this PR does / why we need it:
The current template will not build against canary release as it will fail with. This PR updates the icon to make it compatible.

TS2322: Type '"fa fa-cog"' is not assignable to type '"search" | "repeat" | "anchor" | "link" | "table" | "circle" | "filter" | "info" | "google" | "microsoft" | "github" | "gitlab" | "okta" | "angle-double-down" | "angle-double-right" | ... 172 more ... | undefined'.
     5 | export const plugin = new AppPlugin<{}>().setRootPage(App).addConfigPage({
     6 |   title: 'Configuration',
  >  7 |   icon: 'fa fa-cog',
       |   ^^^^
     8 |   // @ts-ignore - Would expect a Class component, however works absolutely fine with a functional one
     9 |   // Implementation: https://github.com/grafana/grafana/blob/fd44c01675e5497[33](https://github.com/grafana/grafana-plugin-examples/actions/runs/3298636396/jobs/5441011599#step:24:34)70969dfb9e78f173aff7910/public/app/features/plugins/PluginPage.tsx#L157
    10 |   body: AppConfig,

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