feature: support forward cloud requests to edge node's localhost endpoint

[rambohe-ch]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage
/sig storage

/kind feature

What this PR does / why we need it:

1. when components(like prometheus) on cloud nodes usually use NodeIP:Port to collect component(like yurthub) metrics on edge node, but edge components listen on 127.0.0.1:Port instead of NodeIP:Port for security consideration. so we need to add this feature to support proxy cloud requests to localhost endpoint of edge nodes.
2. The way of enable this feature:
   • user can configure the yurt-tunnel-server-cfg configmap, and add specified tcp ports in localhost-proxy-ports field of configmap.
3. for example: yurthub listens on http://127.0.0.1:10267/metrics and yurt-tunnel-agent listens on http://127.0.0.1:10266, user need to configure yurt-tunnel-server-cfg configmap fields as following:

localhost-proxy-ports: "10266, 10267"

Which issue(s) this PR fixes:

Fixes #415

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

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In response to this:

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage
/sig storage

/kind feature

What this PR does / why we need it:

1. when components(like prometheus) on cloud nodes usually use NodeIP:Port to collect component(like yurthub) metrics on edge node, but edge components listen on 127.0.0.1:Port instead of NodeIP:Port for security consideration. so we need to add this feature to support proxy cloud requests to localhost endpoint of edge nodes.
2. The way of enable this feature:
   • user can configure the yurt-tunnel-server-cfg configmap, and add specified tcp ports in localhost-proxy-ports field of configmap.
3. for example: yurthub listens on http://127.0.0.1:10267/metrics and yurt-tunnel-agent listens on http://127.0.0.1:10266, user need to configure yurt-tunnel-server-cfg configmap fields as following:

localhost-proxy-ports: "10266, 10267"

Which issue(s) this PR fixes:

Fixes #415

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

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[rambohe-ch]

/assign @SataQiu @Fei-Guo

[Fei-Guo]

/lgtm
/approve

[openyurt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Fei-Guo, rambohe-ch

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