Add JavaScript coverage analysis

What does this MR do?

• configure teaspoon to calculate test coverage of JavaScript files
• publish result as GitLab pages (thanks @ayufan for the idea)

Are there points in the code the reviewer needs to double check?

• the .gitlab-ci.yml

Why was this MR needed?

• test coverage was not calculated for JavaScript files
• JavaScript wants to be under cover

What are the relevant issue numbers?

#19412 (moved)

Screenshots

spec/teaspoon_env.rb

@@ -149,7 +149,7 @@ Teaspoon.configure do |config|
   # Specify that you always want a coverage configuration to be used. Otherwise, specify that you want coverage
   # on the CLI.
   # Set this to "true" or the name of your coverage config.
-  # config.use_coverage = nil
+  config.use_coverage = true
   # You can have multiple coverage configs by passing a name to config.coverage.
   # e.g. config.coverage :ci do |coverage|
@@ -158,15 +158,15 @@ Teaspoon.configure do |config|
     # Which coverage reports Istanbul should generate. Correlates directly to what Istanbul supports.
     #
     # Available: text-summary, text, html, lcov, lcovonly, cobertura, teamcity
-    # coverage.reports = ["text-summary", "html"]
+    coverage.reports = ["text-summary", "html"]
     # The path that the coverage should be written to - when there's an artifact to write to disk.
     # Note: Relative to `config.root`.
-    # coverage.output_path = "coverage"
+    coverage.output_path = "coverage-javascript"
     # Assets to be ignored when generating coverage reports. Accepts an array of filenames or regular expressions. The
     # default excludes assets from vendor, gems and support libraries.
-    # coverage.ignore = [%r{/lib/ruby/gems/}, %r{/vendor/assets/}, %r{/support/}, %r{/(.+)_helper.}]
+    coverage.ignore = [%r{vendor/}, %r{spec/}]
     # Various thresholds requirements can be defined, and those thresholds will be checked at the end of a run. If any
     # aren't met the run will fail with a message. Thresholds can be defined as a percentage (0-100), or nil.