Take into account rules with empty contition (for tutorial rule)

[epapbak]

Description

All the rules that have metadata.yaml file have a condition field. But the tutorial rule (ccx-rules-ocm)
does not. This change fixes the behaviour where errorContent is not filled correctly if condition field is not
provided.

Fixes #218

Type of change

• Bug fix (non-breaking change which fixes an issue)

Testing steps

• Added new UT for this use case.
• Since tutorial_rule is the one affected, this behaviour will be checked in rule_content integration tests.

[tisnik]

Looks ok (but TBH it would be nice to have some tests for such scenario ;)

[epapbak]

Looks ok (but TBH it would be nice to have some tests for such scenario ;)

It takes 10 minutes max to add them, so I'll do it =)

[codecov-io]

Codecov Report

Merging #217 (7c288d2) into master (ad208d7) will decrease coverage by 0.15%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #217      +/-   ##
==========================================
- Coverage   72.37%   72.22%   -0.16%     
==========================================
  Files           9        9              
  Lines         362      360       -2     
==========================================
- Hits          262      260       -2     
  Misses         81       81              
  Partials       19       19              

Impacted Files	Coverage Δ
content/content.go	86.48% <100.00%> (-0.19%)	⬇️

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