Add peformance reporting sub-module

Problem/Motivation

We semi-frequently receive support requests regarding performance questions.

Adding a sub-module that can report on performance could possibly alleviate some of these requests as site owners would be able to visualize how the s3fs_buckets are responding and gain a better understanding of the factors that may be impacting the site performance.

Areas known to impact performance:

• Latency to any cache services.
• Latency to Database
• Bandwidth to the bucket
• Latency to the bucket
• Latency in the bucket

Database/Cache impact file/directory listing performance, essentially everything related to stat() calls. These may be 'low' latency compared to a direct bucket access, however they can add up in time for operations to complete compared to a direct disk access.
Bucket related metrics impact actual file access above the metadata latency.

The report could also double as providing education, such as describing the bandwidth/latency impact on common operations such as getimagesize() with a 'standard' size file taking X ms to complete.

Steps to reproduce

N/A

Proposed resolution

Create sub-module that provides feedback to administrators about bucket performance.

Remaining tasks

TBD

User interface changes

A new sub-module with new user interface.

API changes

None expected.

Data model changes

None expected.