Replace or remove the "slave" terminology used in a test data

[tlfeng]

Is your feature request related to a problem? Please describe.
Replace or remove the non-inclusive terminology from the code base.

Describe the solution you'd like
There is only 1 usage in the code base that can be replaced or removed, which is a test data:

OpenSearch/modules/mapper-extras/src/test/resources/org/opensearch/index/mapper/metricbeat-6.0.template.json

Line 4601 in 15e9f13

"connected_slaves": {

Document from Elatic that explains the fields in the template: https://www.elastic.co/guide/en/beats/metricbeat/7.10/exported-fields-redis.html

Describe alternatives you've considered
None.

Additional context
Related issue #472

[Rishikesh1159]

I will look into this.

[kartg]

Change merged, backport pending. Leaving this issue open until that is complete.