Logstash Plugin doesn't support string templates

[gianvetter]

Describe the bug
When trying to use Logstash fileds as tenant_id for the loki output plugin, the plugin will not replace the values with the field values.

To Reproduce
Steps to reproduce the behavior:

1. Install Logstash with the Loki Plugin
2. Edit Output config from Logstash tenant_id => "%{[fields][bi_loki_tenant]}"
3. Start Logstash

Expected behavior
The Plugin will replace the %{[fields][bi_loki_tenant]} with the correct values.

Environment:

• Infrastructure: VM
• Deployment tool: Default installation

Fix
I have made already a pull request with the fix #14512

[yehlo]

+1