DUPP-217 Fix welcome notice

[enricobattocchi]

Context

• We want to fix the link in the welcome notice, and change copy references to update notice → welcome notice

Summary

This PR can be summarized in the following changelog entry:

• Fixes an unreleased bug where the link to the privacy policy was broken.

Relevant technical choices:

• We also fixed the labels in the settings to refer to the welcome notice and not to update notice anymore

Test instructions

Test instructions for the acceptance test before the PR gets merged

This PR can be acceptance tested by following these steps:

• install on a clean environment
• see the welcome notice, click on the "Privacy policy" link
  • you should arrive to the page with URL https://yoast.com/privacy-policy/
• visit Settings > Duplicate Post
• navigate to the third tab "Display"
• check that the last checkbox has labels referring to Welcome notice and not to Update notice anymore:
  

Test instructions for QA when the code is in the RC

• QA should use the same steps as above.

QA can test this PR by following these steps:

Impact check

This PR affects the following parts of the plugin, which may require extra testing:

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Documentation

• I have written documentation for this change.

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended

Fixes DUPP-217

[karlijnbok]

Looks good! 👍