feat: allow configuring attachment upload limit (#12835)

## Summary
- add a configurable MAXIMUM_FILE_UPLOAD_SIZE installation setting and
surface it through super admin and global config payloads
- apply the configurable limit to attachment validations and shared
upload helpers on dashboard and widget
- introduce a reusable helper with unit tests for parsing the limit and
extend attachment specs for configurability


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[Codex
Task](https://chatgpt.com/codex/tasks/task_e_6912644786b08326bc8dee9401af6d0a)

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Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>
Co-authored-by: iamsivin <iamsivin@gmail.com>

app/javascript/shared/store/globalConfig.js

@@ -1,4 +1,5 @@
 import { parseBoolean } from '@chatwoot/utils';
+import { resolveMaximumFileUploadSize } from 'shared/helpers/FileHelper';
 
 const {
   API_CHANNEL_NAME: apiChannelName,
@@ -11,6 +12,7 @@ const {
   DIRECT_UPLOADS_ENABLED: directUploadsEnabled,
   DISPLAY_MANIFEST: displayManifest,
   GIT_SHA: gitSha,
+  MAXIMUM_FILE_UPLOAD_SIZE: maximumFileUploadSize,
   HCAPTCHA_SITE_KEY: hCaptchaSiteKey,
   INSTALLATION_NAME: installationName,
   LOGO_THUMBNAIL: logoThumbnail,
@@ -37,6 +39,7 @@ const state = {
   disableUserProfileUpdate: parseBoolean(disableUserProfileUpdate),
   displayManifest,
   gitSha,
+  maximumFileUploadSize: resolveMaximumFileUploadSize(maximumFileUploadSize),
   hCaptchaSiteKey,
   installationName,
   logo,