fix(iOS): Message details not shown in push notifications in some cases

[diegolmello]

Proposed changes

• Changed Secured Push Notification to use SecItemCopyMatching (react-native-keychain) on native iOS side, because MMKV has issues trying to fetch storage in some edge OS cases.
• Removed shared credentials instance
• Changed You have a new message logic to display a single push notification without content, since it's not helpful to fill notification center with it

Issue(s)

Closes #5496

Note: we've been discussing a change on rate limiter for this feature specifically, since some users might receive too many notifications in a short amount of time and that would reach the limit, making push notifications to be displayed as You have a new message still.
Even though we do a reverse fibonacci for retry, the timing might not be enough, since the default time limit is of 5 minutes and the timeframe to fetch notification content is of 30 seconds.

How to test or reproduce

• Enable Hide message content from Apple and Google (and the Gateway, if enabled) (aka Secured Push Notification)
• Receive several push notifications
• They should be displayed correctly on Notification Center

Here's a simple bash to help triggering those push notifications

#!/bin/bash
for i in {1..30}
do
	now=$(date +"%d-%m-%y %H:%M:%S")
	response=$(curl --location --request POST 'https://mobile.rocket.chat/api/v1/chat.postMessage' \
		--header 'content-type: application/json' \
		--header 'x-auth-token: xxx' \
		--header 'x-user-id: xxx' \
		--data-raw '{
				"roomId": "xxxx",
				"msg": "'"$now"'"
		}')

	if [ "$response" -ne 200 ]; then
		echo "[$now] Error: Request failed with status code $response\n" >> error_log.txt
	else
		echo "[$now] Success: Message sent successfully\n"
	fi

	sleep 0.5
done

Screenshots

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves a current function)
• New feature (non-breaking change which adds functionality)
• Documentation update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• I have added necessary documentation (if applicable)
• Any dependent changes have been merged and published in downstream modules

Further comments

CORE-85