Allow adding capability to display alert/announcement in the new UI

[vbaranov]

Description

In the old UI it is managed via SHOW_MAINTENANCE_ALERT (true/false) and MAINTENANCE_ALERT_MESSAGE is for HTML/text message.

Link to the page

https://eth.blockscout.com

Steps to reproduce

1. Go to '...'
2. Click on '...'
3. Scroll down to '...'
4. See error

App version

v.1.9.0

Browser

No response

Operating system

None

Additional information

No response

[isstuev]

use gray alert to display that info

[isstuev]

MAINTENANCE_ALERT_MESSAGE can contain plain text and links, we need to use some template format

[tom2drum]

@vbaranov can you provide an example value for MAINTENANCE_ALERT_MESSAGE for test purposes?

[vbaranov]

@vbaranov can you provide an example value for MAINTENANCE_ALERT_MESSAGE for test purposes?

e.g.

The Sokol Testnet is currently lacking validators. Please consider using <a href="https://eth-goerli.blockscout.com/">Goerli</a> or <a href="https://mumbai.polygonscan.com/">Mumbai</a> for testing purposes.

[tom2drum]

@vbaranov is it OK if we use just one variable NEXT_PUBLIC_MAINTENANCE_ALERT_MESSAGE? If it is present, we will display the message.

[vbaranov]

@vbaranov is it OK if we use just one variable NEXT_PUBLIC_MAINTENANCE_ALERT_MESSAGE? If it is present, we will display the message.

Yeah, I think 1 env var would be pretty much it.

[tom2drum]

And what if we have two alerts to display for indexing blocks and for maintenance, should we show both, one below the other?

[vbaranov]

And what if we have two alerts to display for indexing blocks and for maintenance, should we show both, one below the other?

Yep, one below the other sounds good.