Domains: Fix some usability issues with the custom nameservers controls

[hambai]

Changes proposed in this Pull Request

• Move the notice above and outside the card.
• Change the input placeholders to "eg: ns1.example.com" and "eg: ns2.example.com".
• Make the field label bold

Use custom nameservers (before):

Use custom nameservers (after):

Testing instructions

• Open "Name Servers and DNS" and disable the "Use WordPress.com Name Servers" toggle
• verify that the notice is outside the card, the placeholders are updated and the label is bold

[matticbot]

Test live: https://calypso.live/?branch=update/domain-management-name-servers-usability-fixes

[a8ci18n]

🆗 This change will be queued for retranslation. We'll use the existing translations in the meantime.

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~63 bytes added 📈 [gzipped])

name     parsed_size           gzip_size
domains       +179 B  (+0.0%)      +63 B  (+0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[klimeryk]

Tested and LGTM!

[fditrapani]

The changes look good. Thanks for the updates!