TF-2047 Add adr for sanitize and autolink html when type is text/plain

docs/adr/0030-fix-can-not-see-link-when-type-is-text-plain-in-email-view.md

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+# 30. Fix can not see link when type is text/plain in email view
+
+Date: 2023-08-01
+
+## Status
+
+- Issue: 
+
+[1881](https://github.com/linagora/tmail-flutter/issues/1881)
+[2047](https://github.com/linagora/tmail-flutter/issues/2047)
+
+## Context
+
+- When `Content-Type=Text/Plain` the `url` and `email-addreess` links are not automatically `highlighted`.
+- Some `url` links are `highlighted` when clicking, opening the content in the email view itself does not create a new tab.
+
+## Root cause
+
+- Because we perform `html escape` before creating `autolink`, it makes lost tags undetectable. Moreover, the detect function is ignored in some cases
+
+## Decision
+
+- Use linkify to detect `url/email/text` and return a list of corresponding elements.
+```dart
+   final elements = linkify(inputText);
+```
+
+- If element is `TextElement` we perform html escape for it.
+- If element is `UrlElement` or `EmailElement` we make html link tag (`<a>`) for it.
+```dart
+  String _buildLinkTag({required String link, required String value}) {
+     return '<a href="$link" target="_blank">$value</a>';
+  }
+```
+
+## Consequences
+
+- Accurately detect and fully highlight `url` and `email-address` links in email body when `Content-Type=Text/plain`
+- Automatically open new tab when clicking on `url` link and open composer when clicking on `email-address`