Change OTLP exporter default to HTTP when metrics and logs are added

[pjanotti]

Feature Request

Follow-up to discussion #2855 - more specifically the suggestion to change the default to HTTP when metrics and logs are both covered by the OTLP exporter, see #2855 (reply in thread)

Motivation for the Change
(Copied from the discussion above)
As per latest spec HTTP is preferred over gRPC, see https://github.com/open-telemetry/opentelemetry-specification/blob/ce50e4634efcba8da445cc23523243cb893905cb/specification/protocol/exporter.md?plain=1#L111-L114 and respective PR discussion: open-telemetry/opentelemetry-specification#1969

There is an exception for already released SDKs but I would like to consider a change for the following reasons:

1. Anecdata: most usage of OTLP is with HTTP (easier to get correct configuration for load balancers, proxies, etc)
2. For .NET auto-instrumentation the dependency challenges of earlier versions are harder to deal with, see OTLP Exported as default for .NET (Core) opentelemetry-dotnet-instrumentation#343
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This change should wait for a major bump of the exporter since it is a breaking change.

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