Fix empty JSON output to return "[]" instead of "{}"

[ampandey-hub]

When no data collectors are configured, 'rhc collector list --format json'
and 'rhc collector timers --format json' output {} (empty JSON object).
Since collectors are a list, the correct empty value is [] (empty array).

Fix:

Changed two locations that explicitly print {} to print [] instead:

• cmd/rhc/collector_cmd.go — collectorListAction
• internal/ui/collector.go — printMachineReadable

How I tested

1. Built rhc and rhc-server from source on RHEL 10 (x86_64)
2. Started rhc-server with an empty /usr/lib/rhc/collectors/ directory
3. Before fix: rhc collector list --format json → {}
4. Before fix: rhc collector timers --format json → {}
5. After fix: rhc collector list --format json → []
6. After fix: rhc collector timers --format json → []

Resolves: RHEL-216725

[Archana-PandeyM]

Thanks for the contribution! The CI is currently failing because the commit message is missing the conventional commit category/type (fix:, feat:, test:, etc.).

Could you please amend the commit message to something like:

fix: return empty JSON array for collector list

Once updated, the commit-pipeline check should pass.
to learn about conventional commit https://www.conventionalcommits.org/en/v1.0.0/

[Archana-PandeyM]

/packit test

[Archana-PandeyM]

/packit build

[Archana-PandeyM]

/packit build