TF-2610 Add adr for logic display attachments in email

Signed-off-by: dab246 <tdvu@linagora.com>

docs/adr/0038-logic-for-displaying-attachment-types-in-emails.md

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+# 38. Logic for displaying `attachment` types in emails
+
+Date: 2024-02-20
+
+## Status
+
+Accepted
+
+## Context
+
+- The logic for displaying `attachments` while reading emails is complex
+- Avoid unwanted loss of `attachments` with each new version release
+
+## Decision
+
+Brief the logic flows to make it easier to track changes during `attachment` display in emails:
+
+1. External attachments: Displayed as files outside the email content
+
+- Display is only allowed when one of the following conditions is met:
+  - `cid is NULL` AND `not in htmlBody` AND `does not satisfy this condition mimeType = 'application/rtf' && disposition = 'inline'`
+  - `disposition != 'inline'` AND `not in htmlBody` AND `does not satisfy this condition mimeType='application/rtf' && disposition = 'inline'`
+
+2. Inline attachments: Displayed within the email body
+
+- Display is only allowed when the following conditions are met:
+  - `cid is not NULL` AND `disposition = 'inline'`
+
+## Consequences
+
+- Any changes to attachment display while reading emails should be updated in this ADR.