Configure download settings for standalone Elastic Agent upgrades

The agent.download section of the elastic-agent.yml config file contains settings for where to download and store artifacts used for Elastic Agent upgrades.

Setting	Description
`sourceURI`	(string) Path to the location of artifacts used during Elastic Agent upgrade.
`target_directory`	(string) Path to the directory where download artifacts are stored.
`timeout`	(string) The HTTP request timeout in seconds for the download package attempt.
`install_path`	(string) The location of installed packages and programs, as well as program specifications.
`retry_sleep_init_duration`	(string) The duration in seconds to sleep for before the first retry attempt.
`auth.username` The Elastic Stack includes Elastic's core products such as Elasticsearch, Kibana, Logstash, and Beats. Availability Generally available since 9.4 This functionality is generally available and ready for production usage. Unless stated otherwise on the page, this functionality is available when your Elastic Stack is deployed on Elastic Cloud Hosted, Elastic Cloud Enterprise, Elastic Cloud on Kubernetes, and self-managed environments. This documentation corresponds to the latest patch available for each minor version. If you're not using the latest patch, check the release notes for changes.	(string) Username for HTTP Basic authentication to the artifact registry. Must be set together with `auth.password`, and is mutually exclusive with `auth.api_key`.
`auth.password` The Elastic Stack includes Elastic's core products such as Elasticsearch, Kibana, Logstash, and Beats. Availability Generally available since 9.4 This functionality is generally available and ready for production usage. Unless stated otherwise on the page, this functionality is available when your Elastic Stack is deployed on Elastic Cloud Hosted, Elastic Cloud Enterprise, Elastic Cloud on Kubernetes, and self-managed environments. This documentation corresponds to the latest patch available for each minor version. If you're not using the latest patch, check the release notes for changes.	(string) Password for HTTP Basic authentication to the artifact registry. Must be set together with `auth.username`, and is mutually exclusive with `auth.api_key`.
`auth.api_key` The Elastic Stack includes Elastic's core products such as Elasticsearch, Kibana, Logstash, and Beats. Availability Generally available since 9.4 This functionality is generally available and ready for production usage. Unless stated otherwise on the page, this functionality is available when your Elastic Stack is deployed on Elastic Cloud Hosted, Elastic Cloud Enterprise, Elastic Cloud on Kubernetes, and self-managed environments. This documentation corresponds to the latest patch available for each minor version. If you're not using the latest patch, check the release notes for changes.	(string) API key sent in the `Authorization: ApiKey <api-key>` header. Mutually exclusive with `auth.username` and `auth.password`. If both are configured, `auth.api_key` takes precedence.
`auth.headers` The Elastic Stack includes Elastic's core products such as Elasticsearch, Kibana, Logstash, and Beats. Availability Generally available since 9.4 This functionality is generally available and ready for production usage. Unless stated otherwise on the page, this functionality is available when your Elastic Stack is deployed on Elastic Cloud Hosted, Elastic Cloud Enterprise, Elastic Cloud on Kubernetes, and self-managed environments. This documentation corresponds to the latest patch available for each minor version. If you're not using the latest patch, check the release notes for changes.	(list) Custom HTTP headers sent to the artifact registry on every request. Each entry is an object with `key` and `value` fields.