import shim-rune with a clean base from IC project about enclave-cc HOT 4 CLOSED

Current Status：

1. shim-rune rebase on containerd cc-main branch.
2. Remove unrelated functions in the shim, such as epm, image signature, etc.
3. In the shim create and start APIs, add the function of distinguishing pod_sandbox and pod_container according to the configuration file, and use rune to start the oci bundle (a demo of occlum-hello) successfully when starting pod_sandbox. However, some functions still need to continue to improve, such as exec and log support etc.
4. After adding cri_handle=cc in the configuration file of containerd, the pull image request of cri will call the to pull image of shim-rune, then call the pull image function of enclave-agent container. Right now, enclave-agent is not ready. After the enclave agent is ready, we will debug the pull image function between shim-rune and enclave-agent.

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The patches about shim-rune have been committed to inclavare containers repo with pr. After the internal preliminary review and debugging with the agent enclave based on Occlum NGO about unix socket communication, these patches will be pushed to the enclave-cc repo

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Adding unit tests for shim-rune

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#17 has been merged

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