SKS-1825: Set the default APIGroup and Kind for IPPool CR used in ElfMachineTemplate

[haijianyang]

Issue

简化 IPPool 的配置，默认情况下只需要配置 IPPool name 即可，可以不填写 apiGroup 和 kind。

Change

CAPE 当前使用 ipam.metal3.io IPPool 作为默认的 IP Pool，在 ElfMachineTemplate webhook 默认设置即可，这样创建出来的 ElfMachine 会自动使用默认的 IPPool 配置。

测试

1.ElfMachineTemplate 未设置 apiGroup 和 kind 的 IPPool

  network:
    devices:
    - addressesFromPools:
      - name: ip-pool-node

2. 观察到 addressesFromPools 被设置了 ipam.metal3.io 和 IPPool

  network:
    devices:
    - addressesFromPools:
      - apiGroup: ipam.metal3.io
        kind: IPPool
        name: ip-pool-node

3. 创建出来的 ElfMachine 的 addressesFromPools 设置了ipam.metal3.io 和 IPPool

[codecov]

Codecov Report

Attention: Patch coverage is 51.61290% with 15 lines in your changes are missing coverage. Please review.

Project coverage is 60.00%. Comparing base (1ed0e13) to head (4db1469).

Files	Patch %	Lines
webhooks/elfmachinetemplate_webhook_mutation.go	51.61%	12 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #172      +/-   ##
==========================================
+ Coverage   59.79%   60.00%   +0.20%     
==========================================
  Files          20       21       +1     
  Lines        3699     3730      +31     
==========================================
+ Hits         2212     2238      +26     
+ Misses       1339     1338       -1     
- Partials      148      154       +6     

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