Backport PR #16485 to 8.15 branch, original message:

Release notes

[rn:skip]

What does this PR do?

The LogStash::Util::SubstitutionVariables#replace_placeholders was recently changed, and starting from Logstash 8.15.1 it requires a new argument (refine).
Considering plugins might be using this method internally (e.g: logstash-input-azure_event_hubs), we should make the new argument optional, so existing usages won't break due this change.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files (and/or docker env variables)
• I have added tests that prove my fix is effective or that my feature works

How to test this PR locally

Related issues

• Relates Azure EventHubs Input plugin fails to initialize on Logstash v8.14.x, works in 8.13.x logstash-plugins/logstash-input-azure_event_hubs#91