I gave it a closer look and unfortunately, I cannot accept the proposed solution.

As you may know, there is a limit to the maximum length of the message - 4096 of UTF-16 characters. The URL, especially when it's a link provided by a cloud provider, can be very long (200-300 characters). Also, in the case of multiple alerts in a group, there could be multiple images for the message. Appending them to the message as text will likely make them truncated, which is no better than dropping them altogether. Also, from a perception standpoint, long URLs are not useful and clutter the message, especially when they go one after another.

I can think of an alternative solution - the request model of sendMessage API offers field entities (see https://core.telegram.org/bots/api#sendmessage). It allows clients to implement some WYSIWYG capabilities and format the plain text message. For example

curl --location 'https://api.telegram.org/bot$BOT_TOKEN/sendMessage' \
--form 'chat_id="$CHAT_ID"' \
--form 'entities="[{\"type\":\"text_link\", \"offset\": 10, \"length\": 7, \"url\":\"http://grafana.com\"}]"' \
--form 'text="Hello, 🎉 Grafana\!"'

produces the following message

This approach will let us save a lot of space in the message, and for example append screenshots like

.... Screenshots: [1],[2],[3]

where [1] is a clickable link.

However, there is a downside too - this approach works only when parse_mode is not specified. However, the integration supports different formats such as HTML or Markdown. So, can't use entities in those cases. I think this is ok if we provide some alternatives (does not have to be in this PR).
Ideally, in such a configuration, we can populate template data with URLs. There are already fields in the template data model

Actually, I think I can accept PR that just sets the ImageURL field in template data, and leaves it up to the custom template to include the URL in the message.