Update page on custom interfaces

[kacperbojakowski-3di]

Updated the article "Implementing custom interfaces - how to" as approved by Geoff and 3di.

Description

Related to: ros2/ros2#1725

Updated the custom interfaces how-to page by replacing the old single-package tutorial with the new revised tutorial, and updated the TOC to add the new page entry and remove/replace the old one (incl. the Beginner-Client-Libraries tutorial list).

Did you use Generative AI?

No.

Additional Information

Documentation updates from 3di Information Solutions, agreed with Geoff and Tully.

[kscottz]

@kacperbojakowski-3di

You have some liner errors to address.

source/How-To-Guides/Single-Package-Define-And-Use-Interface.rst:173: Each sentence must start on a new line. Break between "a." and "In your workspace" (sentence-count)
source/How-To-Guides/Single-Package-Define-And-Use-Interface.rst:174: Each sentence must start on a new line. Break between "b." and "Source the workspace" (sentence-count)
source/How-To-Guides/Single-Package-Define-And-Use-Interface.rst:213: Each sentence must start on a new line. Break between "c." and "Check the interface" (sentence-count)

[fujitatomoya]

a couple of minor comments. thanks for making contribution.

[fujitatomoya]

this is under how-to section, the title seems redundant for me.

Suggested change

	Implementing custom interfaces - how-to
	=======================================
	Implementing custom interfaces
	==============================

[fujitatomoya]

metadata line is placed inside a :: literal block, which means it will render as a code snippet on the page. If this is intended as visible metadata for readers, a literal block feels like an unusual presentation choice?