Add 'avoid-buggy-ips' support of MetalLB

[HoKim98]

What type of PR is this?
/kind feature

What this PR does / why we need it:

avoid-buggy-ips is a kind of feature of MetalLB, and it has a function to prevent load-balancing of IPs that are practically unavailable such as:

• 192.168.0.0, 192.168.0.255 in 192.168.0.0/24

This feature is disabled in MetalLB by default, but there is no manual in Kubespray.
So when I try to use MetalLB with CIDR IP subnets, these useless IPs are necessarily assigned.

Therefore, I thought that this function should be controllable in Kubespray as well, and I implemented it as follows:

• metallb_avoid_buggy_ips for default IP address pool
• avoid_buggy_ips for additional IP address pools defined in metallb_additional_address_pools

Examples

metallb_enabled: true
metallb_ip_range:
  - 10.5.0.0/16
metallb_avoid_buggy_ips: true  # new feature
metallb_additional_address_pools:
  kube_service_pool_1:
    ip_range:
      - 10.6.0.0/16
    protocol: "bgp"
    auto_assign: false
    avoid_buggy_ips: true  # new feature
  kube_service_pool_2:
    ip_range:
      - 10.10.0.0/16
    protocol: "bgp"
    auto_assign: false
    avoid_buggy_ips: true  # new feature

Separately, I added this to the docs/metallb.md documentation as examples to indicate that it can be used.

Which issue(s) this PR fixes:

Fixes #4158 (MetalLB configuration via Inventory)

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Added 'avoid-buggy-ips' support of MetalLB (`metallb_avoid_buggy_ips` for default IP address pool and `avoid_buggy_ips` for additional IP address pools defined in `metallb_additional_address_pools`) (⚠️/!\ ADD NOTE : As the newly added feature uses the default value of MetalLB as same, there is no side effect for users who do not change it's value)

[k8s-ci-robot]

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[yankay]

[cristicalin]

Hi @kerryeon, please rebase this PR on current master branch to include the CI fix in #9175

[HoKim98]

Sure, I rebased it to the latest commit.

[yankay]

/lgtm

[oomichi]

Thanks for your contribution.

/ok-to-test
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: kerryeon, oomichi

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