feat(query): support settings admin api for global level settings

[zhang2014]

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Summary

feat(query): support settings admin api for global level settings

curl -XGET 'http://127.0.0.1:8080/v1/tenants/test_tenant/settings'    
curl -XPOST 'http://127.0.0.1:8080/v1/tenants/test_tenant/settings/max_threads' -H "Content-Type: application/json" --data "\"2\""
curl -XDELETE 'http://127.0.0.1:8080/v1/tenants/test_tenant/settings/max_threads'

• Fixes #[Link the issue here]

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - Explain why

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

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This change is 

[TCeason]

LGTM. cc @youngsofun Maybe should have a look.