Support using direct ufs uri when dora is disabled

[Jackson-Wang-7]

What changes are proposed in this pull request?

Implement some functions when Dora is disabled, so the client can access UFS directly without dora cluster.

Why are the changes needed?

Support the alluxio client using UFS URI to access UFS directly

Does this PR introduce any user facing changes?

[huanghua78]

What do you mean by "Dora is disabled"? I don't think Dora can be disabled. Please clarify this with more details.

[Jackson-Wang-7]

@huanghua78 @beinan When you want to use alluxio client to access UFS directly and dora cluster is not involved in, we can use dora.enabled=false to bypass DoraCacheFileSystem. That's what we want to do in only-localcache sdk case and the related code change are in this PR. If you want to combine the client cache and system cache, you can still choose alluxio.user.client.cache.enabled=true and alluxio.dora.enabled=true.

[huanghua78]

@huanghua78 @beinan When you want to use alluxio client to access UFS directly and dora cluster is not involved in, we can use dora.enabled=false to bypass DoraCacheFileSystem. That's what we want to do in only-localcache sdk case and the related code change are in this PR. If you want to combine the client cache and system cache, you can still choose alluxio.user.client.cache.enabled=true and alluxio.dora.enabled=true.

I see. Thanks for this explanation.