Marketplace: Add empty page for plans

[candy02058912]

Proposed Changes

• Adds a new /plugins/plans/:site route with empty content.

Testing Instructions

• Visit http://calypso.localhost:3000/plugins/plans/testing705633960.wordpress\com with your own test site in the url
• View the new (empty) plans page:
  
• Confirm plugin details pages still load as this shares a similar route pattern

Related to #67574

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-42844

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-42844&env=jetpack

[matticbot]

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

Sections (~115 bytes added 📈 [gzipped])

name     parsed_size           gzip_size
plugins       +704 B  (+0.1%)     +115 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.

[a8ci18n]

This Pull Request is now available for translation here: https://translate.wordpress.com/deliverables/7525248

Thank you @candy02058912 for including a screenshot in the description! This is really helpful for our translators.

[a8ci18n]

Translation for this Pull Request has now been finished.