Fallback-aware failure handling - make sure snippet with enabled fall…

[scypio]

…back is processed

Implementation of Knotx/knotx#466 in Template Engine

Description

Allows snippets with misconfigured template engine to be processed further by knotx if they have a fallback strategy assigned. Added relevant integration test

Motivation and Context

see Knotx/knotx#466

Screenshots (if appropriate)

Upgrade notes (if appropriate)

N/A

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

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