Make email for unsuccessful processing a license usage file more transparent

Problem

Follow-up on discussion in #4812 (comment 1246115155).

The email a customer receives for an unsuccessful processing of their license usage file to the renewals service is too generic and does not specify any reason why it was unsuccessful.

Proposal

Provide a reason in the email why the processing failed. While it might not help the customer much, it will help a lot on the debug side for Support and engineering.

Errors to address

  1. Incorrect mime-type - related to https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/5845
    1. Identify when a mime-type other than those now supported is used
  2. File already recorded - we already have seat link data stored no longer relevant, error resolved with https://gitlab.com/gitlab-org/customers-gitlab-com/-/merge_requests/7879
  3. No license file attached to the email (code). See details here: https://gitlab.com/gitlab-org/customers-gitlab-com/-/issues/5961#note_1504884317
  4. Others?

Text Proposal

Current email text for reference 
<%= ('Hello ' + @customer.full_name).strip %>,

We had a problem trying to process your license usage file.

You can check your account details on the Customers Portal: https://customers.gitlab.com.

As part of your paid subscription you are entitled to support. Before you submit your first GitLab support ticket,
set up your authorized support contacts https://about.gitlab.com/support/managing-support-contacts/
For more information on how to do this, review our support documentation page https://about.gitlab.com/support
or visit our support portal <%= gitlab_support_url%>

To contact support, visit our support portal at https://support.gitlab.com.

If you have other questions or concerns, please contact us at https://about.gitlab.com/contact.

Summary Proposal

Add a new section that lists the problem and a sentence as to how to resolve.

<%= ('Hello ' + @customer.full_name).strip %>,

We had a problem trying to process your license usage file, see details below.

* **Problem:** SUMMARY OF PROBLEM
* **Details:** DESCRIPTION OF PROBLEM AND HOW TO RESOLVE

You can check your account details on the Customers Portal: https://customers.gitlab.com.

As part of your paid subscription you are entitled to support. Before you submit your first GitLab support ticket,
set up your authorized support contacts https://about.gitlab.com/support/managing-support-contacts/
For more information on how to do this, review our support documentation page https://about.gitlab.com/support
or visit our support portal <%= gitlab_support_url%>

To contact support, visit our support portal at https://support.gitlab.com.

If you have other questions or concerns, please contact us at https://about.gitlab.com/contact.

Result

The reason for the unsuccessful processing is better understood by the customer and easier for them to self-resolve .

Support Priority Score: (-, -, -, -, -, -, -, -, -, -, -) => 4

Edited by Courtney Meddaugh