Embed templates interpolate regex captures from user-authored article
URLs into HTML attribute values. CommonMark's angle-bracket link
destination syntax allows characters that the capture regexes don't
filter, so the unescaped substitution could produce malformed attribute
output. Escaping at substitution time keeps the render deterministic
regardless of the URL.
### How was this tested?
Added specs.
Fixes [CW-6934](https://linear.app/chatwoot/issue/CW-6934/)
Co-authored-by: Sony Mathew <sony@chatwoot.com>
Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>