Assume distribution_version is set to opensearch for OpenSearch source

Is your feature request related to a problem? Please describe.
The opensearch source attempts to auto detect by calling the GET / API if the source is an opensearch or elasticsearch cluster. Sometimes, clusters have spoofed responses that impersonate something they are not, and this can lead to failures without the distribution version being set.

Describe the solution you'd like
To handle this more gracefully, if distribution_version is not set, and the attempts to call the GET / API fail for both the opensearch and elasticsearch clients, the opensearch source should act as if the distribution_version is set to OpenSearch, and continue

Describe alternatives you've considered (Optional)
A clear and concise description of any alternative solutions or features you've considered.

Additional context
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