Change expected `coverage` structure for CI configuration YAML file

Instead of using:
`coverage: /\(\d+.\d+%\) covered/`

This structure must be used now:
```
coverage:
  output_filter: /\(\d+.\d+%\) covered/`
```

The surrounding '/' is optional.

lib/ci/gitlab_ci_yaml_processor.rb

@@ -61,7 +61,7 @@ module Ci
         allow_failure: job[:allow_failure] || false,
         when: job[:when] || 'on_success',
         environment: job[:environment_name],
-        coverage_regex: job[:coverage],
+        coverage_regex: job[:coverage][:output_filter],
         yaml_variables: yaml_variables(name),
         options: {
           image: job[:image],

lib/gitlab/ci/config/entry/coverage.rb

@@ -8,17 +8,27 @@ module Gitlab
         class Coverage < Node
           include Validatable
 
+          ALLOWED_KEYS = %i[output_filter]
+
           validations do
-            validates :config, regexp: true
+            validates :config, type: Hash
+            validates :config, allowed_keys: ALLOWED_KEYS
+            validates :output_filter, regexp: true
           end
 
-          def value
-            if @config.first == '/' && @config.last == '/'
-              @config[1...-1]
+          def output_filter
+            output_filter_value = @config[:output_filter].to_s
+
+            if output_filter_value.start_with?('/') && output_filter_value.end_with?('/')
+              output_filter_value[1...-1]
             else
-              @config
+              value[:output_filter]
             end
           end
+
+          def value
+            @config.merge(output_filter: output_filter)
+          end
         end
       end
     end

lib/gitlab/ci/config/entry/job.rb

@@ -72,7 +72,7 @@ module Gitlab
                description: 'Environment configuration for this job.'
 
           entry :coverage, Entry::Coverage,
-               description: 'Coverage scanning regex configuration for this job.'
+               description: 'Coverage configuration for this job.'
 
           helpers :before_script, :script, :stage, :type, :after_script,
                   :cache, :image, :services, :only, :except, :variables,

lib/gitlab/ci/config/entry/legacy_validation_helpers.rb

@@ -31,7 +31,7 @@ module Gitlab
           def validate_regexp(value)
             Regexp.new(value)
             true
-          rescue RegexpError
+          rescue RegexpError, TypeError
             false
           end
 
@@ -39,7 +39,7 @@ module Gitlab
             return true if value.is_a?(Symbol)
             return false unless value.is_a?(String)
 
-            if value.first == '/' && value.last == '/'
+            if value.start_with?('/') && value.end_with?('/')
               validate_regexp(value[1...-1])
             else
               true