Fix: notify locale on successful pipeline

What does this MR do and why?

Reason

Right now the email template for successful pipeline notification can only be sent in English

Result

in this MR I updated the template with i18n enabled strings instead of hardcoded strings. After this MR it will be able to send languages the user prefers.

/cc @prajnamas @orozot @qk44077907

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Triggered by API

Triggered on demand

You may visit this link on your local instance:

http://[your.gdk.com]/rails/mailers/notify/pipeline_success_email

You might not be able to see the screenshot that was not triggered by API, you need to find any available project on your gdk and manually trigger a pipeline (even though it will not run) then refresh the page you can see the updates.

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