Add per-namespace-per-shard scope in ResourceExhaustedScope (#649)

**What changed?**
Add per-namespace, per-shard scope and per-execution scope in
ResourceExhaustedScope.

**Why?**
We return RESOURCE_EXHAUSTED_SCOPE_NAMESPACE resource exhausted error
from persistence client when per-namespace, per-shard limit of a
namespace is exhausted.
But this causes confusion in metrics. There is no way to distinguish
this error from per-namespace persistence limit exceeded errors. Adding
this new scope for these errors will make it clear.

Similary RESOURCE_EXHAUSTED_SCOPE_EXECUTION can be used to return
per-execution resource exhausted errors like the lock timeout in mutable
state cache.

Author: prathyushpv