Add cluster stats for ORCA load reports processing in `Router::Filter`.

[efimki]

Adding cluster stat counters stats for ORCA load reports processing in Router::Filter:

• upstream_orca_lb_success - Host LB Policy callback success.
• upstream_orca_lb_error - Host LB Policy callback error.
• upstream_orca_lrs - ORCA load report added to LRS metrics.

Risk Level: LOW Testing: bazel test //test/common/router:router_test Docs Changes: None

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:cat:

Caused by: https://github.com/envoyproxy/envoy/pull/42463 was opened by efimki.

see: more, trace.

[efimki]

@adisuissa WDYT about adding some cluster metrics for ORCA load report processing in Router::Filter?