Bulk executor cache

[ealsur]

Pull Request Template

Description

Currently we are maintaining the Executor instance as part of the Container instance, but the Container instance is really too ephemereal and users could be calling GetContainer multiple times for the same container across their code, in which case we would end up creating a lot of Executor instances that would not be used or worse, the desired performance effect would not be reached if the concurrent operations are using different Container instances for the same container name.

This PR introduces a cache at the Client level to have one Executor per Container based on the Link. This way, Executor instances can be shared across Container instances representing the same container and hence, achieving the desired performance benefit even when the user is calling GetContainer from concurrent threads.

The Executor cache is maintained in sync when DeleteContainer operations are issued, by removing cache entries for deleted containers.

The cache is also tied to the CosmosClient lifetime, when the client is disposed, the Executor cache and instances get disposed.

[kirankumarkolli]

One more alternative is to include Executor at Partition cache.
PartitionCache is global and we just need to ensure refreshed doesn't throw away existing ones.
It might need to interact with HA layer.

On similar notes CollectionCache can also be leveraged. Its very specific to SDK code.
Thoughts?

[kirankumarkolli]

Update from offline sync-up:

1. Extending existing stateless caches is non-trivial -> new cache is good
2. Bulk needs to cover Gone with NameCacheStale in Retry Policies
3. Prefer AsyncCache< Executors>

[kirankumarkolli]

Extending existing stateless caches is non-trivial -> new cache is good
Bulk needs to cover Gone with NameCacheStale in Retry Policies
Prefer AsyncCache< Executors>

[ealsur]

@kirankumarkolli Retry policy for NameStaleCache is a separate PR, see #859

Updated PR to use AsyncCache

[kirankumarkolli]

No contract change but contract file touched.

[kirankumarkolli]

Its worth a mention in release notes.