[Newsletter] Fixing the customer subscribing from different stores

[eduard13]

Description (*)

This PR fixes the customer subscription from different stores.

Fixed Issues (if relevant)

1. Newsletter subscription does not set the correct store_id if already subscribed. Not Fixed in 2.3-dev #19172: Newsletter subscription does not set the correct store_id if already subscribed. Not Fixed in 2.3-dev

Manual testing scenarios (*)

1. Create 2 stores: A(default) and B
2. Login on the frontend
3. Subscribe to Newsletter (which should be successfully)
4. Switch to store B
5. Subscribe to Newsletter (you get the success message, but the subscription wasn't saved)

For details, please check the task's description.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @eduard13. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me 2.3-develop instance - deploy vanilla Magento instance

For more details, please, review the Magento Contributor Assistant documentation

[eduard13]

@magento-engcom-team give me test instance

[magento-engcom-team]

Hi @eduard13. Thank you for your request. I'm working on Magento instance for you

[magento-engcom-team]

Hi @eduard13, here is your new Magento instance.
Admin access: http://34.228.235.121/pr-19195//admin
Login: admin Password: 123123q

[rogyar]

@magento-engcom-team give me test instance

[magento-engcom-team]

Hi @rogyar. Thank you for your request. I'm working on Magento instance for you

[magento-engcom-team]

Hi @rogyar, here is your new Magento instance.
Admin access: http://34.228.235.121/pr-19195//admin
Login: admin Password: 123123q

[magento-engcom-team]

Hi @eduard13. Thank you for your contribution.
We will aim to release these changes as part of 2.3.1.
Please check the release notes for final confirmation.

[nathanjosiah]

@eduard13 Thank you for your contribution! Unfortunately this PR had to be reverted for 2.3.1 as it created a new bug. To reproduce the new bug with your changes applied:

Precondition
Customer Website with Store View is created

Steps to reproduce

1. Login as Admin User
2. Go to Customers > All Customers
3. Click to Add New Customer
4. Fill all required field
5. In Associate to Website dropdown select Customer Website
6. In Send Welcome Email From dropdown select Customer Store View
7. Click Save Customer
8. Check customer's email box

✅ Expected result:
Welcome email is present, sent from Customer Website

❌ Actual result
Welcome email is present, sent from Main Website

If you wish to submit a new PR to fix both issues please reference our internal issues MAGETWO-98377, ENGCOM-3460, and MC-15307