Document query URL redaction

[pellared]

Hotfix for OpenTelemetry.Instrumentation.AspNetCore to 1.8.1
Hotfix for OpenTelemetry.Instrumentation.Http to 1.8.1

I find it bad that hotfixes change the default behavior in a breaking way.
See: open-telemetry/opentelemetry-dotnet#5541

We should add code to set OTEL_DOTNET_EXPERIMENTAL_ASPNETCORE_DISABLE_URL_QUERY_REDACTION and OTEL_DOTNET_EXPERIMENTAL_HTTPCLIENT_DISABLE_URL_QUERY_REDACTION to true if these are unset.

We miss docs for these env vars.

Our changelog should also be improved to include changes in the emitted telemetry.

Originally posted by @pellared in #3372 (comment)

[pellared]

I find it bad that hotfixes change the default behavior in a breaking way.
See: open-telemetry/opentelemetry-dotnet#5541

We confirmed with our Product Manager that this breaking change this is not acceptable for us.
We decided to not rush and discuss the mentioned issue further.
We plan to join the OTel SemConv SIG meeting next Monday to discuss the impact of this change.
We are not planning to make a release of OTel .NET Automatic Instrumentation before that.

CC @MikeGoldsmith @lmolkova @akubik-splunk @mtwo

[pellared]

According to OTel Specification such change is allowed. More: open-telemetry/opentelemetry-dotnet#5541 (comment)

From my perspective we should only document the new env vars and mention in the changelog the changed behavior (and new env vars).