chore: add deprecation note for DNT (#4020)

The PR adds a deprecation note to remove DNT as part of the next major
release.
The decision is captured
[here](https://coveord.atlassian.net/browse/LENS-1502?focusedCommentId=764668).
The main drivers were:
- DNT is an outdated standard. Newer standards like GPC have been
introduced. We don't believe it's Coveo's role to update libraries to
adhere to the latest standards?
- Privacy standards differ around the world. Baking a single privacy
stance into Coveo's libraries and apis will be overly restrictive in
certain geographies.

**Aside**
I tried to adjust the logic in headless to only apply DNT if the
analyticsMode is `legacy`. However, this required changing an action to
an thunk. The signature change created multiple typescript errors, and
so seems like it's breaking. I changed course to add a deprecation note
instead. With the v3 release around the corner, it seems less risky to
simply remove the `doNotTrack` function rather than making a signature
change.

---------

Co-authored-by: Louis Bompart <lbompart@coveo.com>

packages/headless/src/app/engine.ts

@@ -198,7 +198,8 @@ function getUpdateAnalyticsConfigurationPayload(
     apiBaseUrl,
   };
 
-  if (doNotTrack()) {
+  // TODO KIT-2844
+  if (payloadWithURL.analyticsMode !== 'next' && doNotTrack()) {
     logger.info('Analytics disabled since doNotTrack is active.');
     return {
       ...payloadWithURL,

packages/headless/src/features/configuration/configuration-actions.ts

@@ -8,7 +8,6 @@ import {
 } from '@coveo/bueno';
 import {createAction} from '@reduxjs/toolkit';
 import {IRuntimeEnvironment} from 'coveo.analytics';
-import {doNotTrack} from '../../utils/utils';
 import {
   nonEmptyString,
   validatePayload,
@@ -207,9 +206,6 @@ const analyticsConfigurationSchema: SchemaDefinition<
 export const updateAnalyticsConfiguration = createAction(
   'configuration/updateAnalyticsConfiguration',
   (payload: UpdateAnalyticsConfigurationActionCreatorPayload) => {
-    if (doNotTrack()) {
-      payload.enabled = false;
-    }
     return validatePayload(payload, analyticsConfigurationSchema);
   }
 );

packages/headless/src/utils/utils.ts

@@ -45,9 +45,15 @@ export function getObjectHash<T>(obj: T) {
 }
 
 const doNotTrackValues = new Set(['1', 1, 'yes', true]);
+// TODO KIT-2844
 
 /**
  * Logic copied from coveo.analytics.
+ *
+ * @deprecated Starting with Event Protocol, Coveo will no longer respect the DNT standard.
+ * Instead, we will provide implementers with documentation on privacy best-practices, letting
+ * them decide which standards to respect.
+ * For more context behind the decision, see: https://coveord.atlassian.net/browse/LENS-1502
  */
 export function doNotTrack() {
   if (typeof navigator === 'undefined' || typeof window === 'undefined') {