feat: support local config file watcher of client and server

[ozline]

• feat: support local file config of client and server

• del: .DS_Store

• add: license header

• fix: staticcheck error report

• fix: use NewRetryContainerWithPercentageLimit to create retry container

• docs: correct sentence placement

• fix: use individual module in example folder

• feat: merge ClientWatcher and ServerWatcher into ConfigWatcher

• fix: update error judgment of utils.PathExists()

• docs: update README.md

• chore: move example folder to kitex-contrib/example

• fix: set alias for client/server to avoid same package name

• fix: delete useless log

• fix: add recover for new goroutines to avoid crashing

• add: comments for exported symbols

• del: monitor/key.go

• feat: separating filewatch and configmonitor

• docs: update README.md

• fix: README.md usage import package error

• add: monitor test cases

• test: add entire progress test

• fix: add mutex for start/stop file watching

• fix: staticcheck error report

• fix: multiple clients can listen to the same key without affecting each other

• delete: remove the gomock module and use self-made simple mock instead

• feat: upgrade required module version

• fix: remove redundant golang versions in workflow tests

• add: use example of this lib

• fix: README_CN.md spell error

• chore: README add supported file types

• fix: panic when type assertion fails at runtime

• chore: add log while callback is nil

• fix: README.md lib name error

• chore: add licenses

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: li-jin-gou, ozline

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