WIP: Telemetry documentation

cppTango:

Requires opentelemetry-cpp and other libraries, see https://gitlab.com/tango-controls/cppTango/-/blob/main/INSTALL.md?ref_type=heads#cmake-variables.

Environment variables:

• TANGO_TELEMETRY_TRACES_ENDPOINT, defaults to Tango::telemetry::Configuration::DEFAULT_GRPC_TRACES_ENDPOINT for gRPC and Tango::telemetry::Configuration::DEFAULT_HTTP_TRACES_ENDPOINT for HTTP. Can be cout or cerr for console.
• TANGO_TELEMETRY_LOGS_ENDPOINT, defaults to Tango::telemetry::Configuration::DEFAULT_GRPC_LOGS_ENDPOINT for gRPC and Tango::telemetry::Configuration::DEFAULT_HTTP_LOGS_ENDPOINT for HTTP. Can be cout or cerr for console.
• TANGO_TELEMETRY_ENABLE: defaults to "off" if not present, can be one of "on"/"off"
• TANGO_TELEMETRY_KERNEL_ENABLE: defaults to "off" if not present, can be one of "on"/"off"
• TANGO_TELEMETRY_TRACES_EXPORTER: defaults to "console", can be one of "grpc", "http", "console", or "off".
• TANGO_TELEMETRY_LOGS_EXPORTER: defaults to "console", can be one of "grpc", "http", "console", or "off".