admin log:add log level filter

[dormanze]

Community Contribution License

All community contributions in this pull request are licensed to the project maintainers under the terms of the Apache 2 license. By creating this pull request I represent that I have the right to license the contributions to the project maintainers under the Apache 2 license.

Description

When I run the admin log command to view the server logs, I find that some empty logs are often printed. For example:

Motivation and Context

We want to view the event logs of the minio, but the printed result is empty. ps:The event-level logs of nodes that fall out of the cluster and then rejoin the cluster are helpful.

How to test this PR?

mc admin log myminio --level all

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [x] Optimization (provides speedup with no functional changes)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [ ] Fixes a regression (If yes, please add commit-id or PR # here)
• [ ] Unit tests added/updated
• [ ] Internal documentation updated
• [ ] Create a documentation update request here