feat: support sending events when app move to background

[zhu-xiaowei]

Description

1. add background task for sending request when app move to background.
2. change event log to prettier format.

General Checklist

• Added new tests to cover change, if needed
• Build succeeds using Swift Package Manager
• All unit tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.05 🎉

Comparison is base (3dfe309) 94.54% compared to head (35c0449) 94.60%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #21      +/-   ##
==========================================
+ Coverage   94.54%   94.60%   +0.05%     
==========================================
  Files          33       33              
  Lines        1669     1686      +17     
==========================================
+ Hits         1578     1595      +17     
  Misses         91       91              

Impacted Files	Coverage Δ
...ckstream/AWSClickstreamPlugin+ClientBehavior.swift	96.05% <100.00%> (ø)
...ndency/Clickstream/Analytics/AnalyticsClient.swift	100.00% <100.00%> (ø)
...pendency/Clickstream/Analytics/EventRecorder.swift	99.13% <100.00%> (+0.14%)	⬆️
...Clickstream/AutoRecord/AutoRecordEventClient.swift	93.18% <100.00%> (+0.05%)	⬆️

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