fix(ci): limit builds on forked PRs, optimize CI workflow

[thenextman]

• Although it's possible to check if we're on a fork (and even to check for dependabot builds by checking github.actor), it's not possible to exclude a job based on a matrix condition. Instead, generate the build matrices dynamically using PowerShell. This allows us to drop the Windows builds in case secrets are not available (e.g. a PR from a fork). A warning will be printed in this case.
• Revert to using secrets.ARTIFACTORY_READ_TOKEN. This token is now available for builds from dependabot.
• Don't bootstrap conan or OpenSSL when building for non-Windows.
• Drop the jetsocat build for the Windows x86 target.

[CBenoit]

Nice dynamic matrix trick

Nit: instead of fix(ci):, there is a commit type ci

ci: limit builds on forked PRs, optimize CI workflow

I use this to put related commits in a "Continuous Integration" section in our changelog: