cypress: Add end to end tests for content rendering

.gitignore

cypress.json

cypress/fixtures/example.json

cypress/fixtures/source-file-extensions.json

cypress/fixtures/source-file-names.json

cypress/integration/content-rendering.spec.js

cypress/plugins/index.js

cypress/utils/index.js

swh/web/config.py

swh/web/settings/tests.py

swh/web/tests/data.py

swh/web/tests/resources/contents/code/LICENSE

swh/web/tests/resources/contents/code/extensions/test.R

swh/web/tests/resources/contents/code/extensions/test.abnf

swh/web/tests/resources/contents/code/extensions/test.adb

swh/web/tests/resources/contents/code/extensions/test.adoc

swh/web/tests/resources/contents/code/extensions/test.ahk

swh/web/tests/resources/contents/code/extensions/test.aj

...tests/resources/contents/code/extensions/test.applescript

swh/web/tests/resources/contents/code/extensions/test.as