Backport of Add the -capture flag to proxy log command. into release/1.8.x

[hc-github-team-consul-core]

Backport

This PR is auto-generated from #4788 to be assessed for backporting due to the inclusion of the label backport/1.8.x.

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Warning automatic cherry-pick of commits failed. If the first commit failed,
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The person who merged in the original PR is:
@LordAbhishek
This person should resolve the merge-conflict(s) by either:

• Manually completing the cherry picks into this branch
• Creating a new branch and manually cherry-picking all commits being backported

merge conflict error: POST https://api.github.com/repos/hashicorp/consul-k8s/merges: 409 Merge conflict []

The below text is copied from the body of the original PR.

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Changes proposed in this PR

• Added -capture flag to proxy log command.
• This will enable user to capture log for given duration and write them to a file in current working dir.
• If -update-level flag is provided along with -capture flag, it will set given new log level, capture the log for given duration and reset the log level to existing one post log capture.
• consul-k8s proxy log <podname> -capture 1m -update-level debug

Signal interrupt handling:

• Here, with existing base command setup, if signal interrupt is received during log capture, it would exit the terminal at an instant, so log levels won't be reset back to existing levels.
• So, to handle the signal interrupt while capturing log, I have modified main.go, commands.go, common/base.go which will handle signal interrupts with the help of a cleanupReqAndCompleted channel for any cli command in consul-k8s.
• With the new setup of common/base.go and main.go, it will reset back the log levels back to previous one, basically main will wait unitll reset.

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Overview of commits

• 80f852e

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