Content Delivery functionality introduced in SDL Tridion Sites 9.1

SDL Tridion Sites 9.1 introduces new Content Delivery features

Health and info check URLs have changed and are configurable
Previously, you could append /info or /health to the end of a base URL http://HOST:PORT, where HOST and PORT identified the location of a Content Delivery microservice, to obtain basic information about the microservice and its health.
Additionally, you can now customize the URL to your liking by editing the new management.context-path property in the application.properties file of the microservice.
Now, the URL to which you append /info or /health is the full microservice URL, say, http://HOST:PORT/content.svc.
Required Elasticsearch version is now 6.7
The supported Elasticsearch version for Experience Optimization is now version 6.7 (both for on-premises setups and for Cloud-based setups). Refer to the following Elasticsearch documentation topics for more about the impact of this change:
Scheduling a cleanup of the State Store database
By setting environment variables on the machine on which Content Deployer runs, you can instruct the system to periodically clean up obsolete records in the State Store database.
Logging of Spring boot messages if log level is set to TRACE
As of this release, the Logback configuration files (logback.xml files) by default contain a logger for Spring boot services. This logs the endpoint mappings. Request mapping is logged under the TRACE log level.
You can now perform a GraphQL query to search separately for titles in any language
Although it was already possible to search the full content of an item to find a title in another language than the default, there is now also a rawLanguageTitle query field that contains specifically a title in the language of your choosing. Accompanying this new field is a new property, indexLanguage, in your locale-to-language mapping file, which maps directly to content.LANGUAGE in the main index, where LANGUAGE is the language in which you are indexing. If you want to add a new language to your Elasticsearch configuration, follow the lead of the other language configurations and be sure to include rawLanguageTitle.