Improve usability and consistency of the network admin email change notices.

[afercia]

Follow up to #66173.

For consistency with the changes in #66173 for the single site user and administration notices, also the network admin change notices should be improved in terms of clarity of the admin notices and usability.

Basically:

• Add an info notice at the top.
• Change the type of the notice in the middle of the page to 'info'.
• Change the cancel link text to 'Cancel request'.
• Provide the link in both notices.
• After clicking the activation link in the confirmation email, add a success notice Network admin email updated..
• Settings saved. should be bold, for consistency with single site settings.

Use of AI Tools

NONE

[afercia]

In ​PR 14247:

• Adds an 'info' admin notice in the Network Settings page when changing the network admin email.
• The notice is similar to the one already rendered on single site.
• The notice at the top is rendered after the 'Settings saved.' one.
• The notice in the middle of the page is now of type 'info'.
• The 'Cancel' link text is now a more meaningful 'Cancel request'.
• The 'Cancel request' link is now rendered in both the admin notices.
• After clicking the activation link in the confirmation email, a success notice Network admin email updated. is rendered at the top of the page.
• Improves the redirect links by using add_query_arg().
• The standard Settings saved. notice text is now bold, for consistency with the single site settings.