Allow downloading artifacts from project specific locations

[cmacknz]

This PR fixes several bugs and makes it possible to download artifacts from the project specific staging areas that feed into the unified release process. This is necessary in the time between a feature freeze and the first snapshot being produced, which historically has been several days.

Examples of project specific URLs are:

• https://artifacts-snapshot.elastic.co/beats/latest/8.11.0-SNAPSHOT.json
• https://artifacts-snapshot.elastic.co/endpoint-dev/latest/8.11.0-SNAPSHOT.json
• https://artifacts-snapshot.elastic.co/fleet-server/latest/8.11.0-SNAPSHOT.json
• https://artifacts-snapshot.elastic.co/prodfiler/latest/8.11.0-SNAPSHOT.json

This also makes the following changes:

• Adds mutexes to shared caches to allow downloads to happen in parallel safely.
• Remove use of the curl package in favor of the stdlib
• Improve logging, both by using less of it and including the name of the resolver that generated the log.

To test this PR, check out https://github.com/cmacknz/elastic-agent/tree/fix-artifacts-api-usage and replace the e2e-testing dependency with this version. The build will succeed, where as it fails on main. The draft PR for this change without the dependency update is elastic/elastic-agent#3273.

To see what the new logging looks like, change to InfoLevel logging instead of FatalLevel in https://github.com/cmacknz/elastic-agent/blob/5c28f4e975748c0f63af9c653124ca4bd4e2a74b/magefile.go#L953

• Relates Elastic Agent relies on artifacts-api for fetching the dependent artifacts when running the packaging elastic-agent#1273

[mergify]

This pull request does not have a backport label. Could you fix it @cmacknz? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.