Preserve operator media captions for Telegram attachments

[mysubcult]

Preserve captions for media messages sent by an operator from Telegram topics and update the bundled Telegram REST API template to pass captions with file API requests.\n\nRelated core PR: LiveHelperChat/livehelperchat#2394

[mysubcult]

Updated to match LiveHelperChat/livehelperchat#2394 feedback.\n\nThe Telegram REST API config now sets suburl_file_skip_ext to gs, so the core can keep this provider-specific caption limitation in back office configuration instead of hardcoding the extension.

[mysubcult]

Rebased this PR on the latest upstream master and reopened it. The functional changes are the same: preserve incoming media captions and set the REST API template skip extension field to gs so sticker-specific behavior remains configuration-driven.

[mysubcult]

Added a small follow-up fix for Telegram GIFs/animations. Telegram reports GIF messages as �nimation, so the command now treats �nimation as a supported media type, stores it as a chat file, and keeps the caption path consistent with other media.