feat: Home page announcement

[novakzaballa]

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Changes

Show an announcement at the top of the home page.
The title, body and link of the annouoncement are provided in the value attribute of the announcement feature flag on our production environment of the Flagsmith Website project.
Example value:

{ 
"id":"announcement-1",
"title":"Master Feature Flags & Progressive Delivery!",
"description":"Join us in London for a hands-on workshop with Dynatrace on feature flags and observability-driven progressive delivery.",
"buttonText":"Save My Seat!",
"url":"https://info.dynatrace.com/emea-uk-dh-progressive-delivery-workshop-flagsmith-22371-registration.html",
"isClosable":true
}

How did you test this code?

This code has been manually tested by setting a JSON value for the announcement feature flag, and verifying that:

• The banner is shown with the correct content
• The button has the right label and when clicked opens a new tab with the right URL
• When dismissed is not being shown anymore to the same user

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Name	Status	Preview	Comments	Updated (UTC)
docs	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 30, 2023 6:02pm
flagsmith-frontend-preview	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 30, 2023 6:02pm
flagsmith-frontend-staging	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 30, 2023 6:02pm

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