OTLPExporter msrv check in CI

[cijothomas]

https://github.com/open-telemetry/opentelemetry-rust/pull/1840/files has explicitly updgraded msrv for otlp exporter. But the CI check is not checking this for OTLP exporter now.

https://github.com/open-telemetry/opentelemetry-rust/blob/main/scripts/msrv.sh#L14-L17

Opening an issue to track adding the msrv check for otlp. It could be done via an env variable to control the version or other ideas are welcome.

[lalitb]

Do we need to bump msrv for opentelemetry-proto too, as that too depends on tonic and prost?

[cijothomas]

closed via #1864