Change config option 'default_suffix' to 'extension' to match other renderers

[Xerkus]

Provide a narrative description of what you are trying to accomplish:

This PR changes config option for resolver default suffix from default_suffix to extension to match plates and twig template renderers.
Related: #64

• Are you creating a new feature?
  • Why is the new feature needed? What purpose does it serve?
    add support for custom template file default suffix #64 introduced a way to configure default suffix using configuration option $config['templates']['default_suffix'] however two other template renderers provided by framework use key extension
    This PR fixes inconsistency inadvertently introduced by add support for custom template file default suffix #64 by making use of extension key.
  • How will users use the new feature?
    By providing alternative suffix in config:

    [
        'templates' => [
            'extension' => 'php',
        ],
    ]

  • Base your feature on the develop branch, and submit against that branch.
  • Add only one feature per pull request; split multiple features over multiple pull requests
  • Add tests for the new feature.
  • Add documentation for the new feature.
    Documentation needs to be added in another repository
  • Add a CHANGELOG.md entry for the new feature.

[michalbundyra]

What about adding E_USER_DEPRECATED when default_suffix is used? It should help with migration.

[Xerkus]

I think it would be a bad idea to do for 'config' service. And I did a release just couple days ago. Missed that inconsistency during review.

[froschdesign]

@Xerkus
I can not found any documentation for this configuration option for zend-view. Only for Plates and Twig:

• https://docs.zendframework.com/zend-expressive/v3/features/template/plates/#configuration-and-factory
• https://docs.zendframework.com/zend-expressive/v3/features/template/twig/#configuration

It would be great if you could add this.

[Xerkus]

@froschdesign i didn't add it yet, I discovered inconsistency when I was preparing a PR for the docs

[froschdesign]

@Xerkus

…I was preparing a PR for the docs

Great! 👍