Add multicast subcommand

[yushoyamaguchi]

Change

This change adds cilium multicast sub command to manage multicast groups and subscribers throughout the cluster

Following commands are added

# show list of multicast group
- cilium multicast list group

# show list of subscribers
- cilium multicast list subscriber --all
- cilium multicast list subscriber --group-ip <group-ip>

# make specified multicast group and add CiliumInternalIP of all cilium nodes to the group in each node
- cilium multicast add --group-ip <group-ip>

# Remove CiliumInternalIP of all cilium nodes from specified multicast group and delete the group in each node
- cilium multicast del --group-ip <group-ip>

This is follow up of #2574

Display example

Additional

As for testing, we will proceed with the implementation of the connectivity test for multicast as described in this issue.(#2615)

Reference

Current way of setup multicast : https://github.com/cilium/cilium/blob/main/Documentation/network/multicast.rst

[harsimran-pabla]

Thank you for the changes; overall, it looks good. A couple of areas that need work are concurrency and error handling.

[maintainer-s-little-helper]

Commit d70128e does not match "Signed-off-by".

Please follow instructions provided in https://docs.cilium.io/en/stable/contributing/development/contributing_guide/#developer-s-certificate-of-origin

[asauber]

I will save a detailed review for after the current round of changes.

[harsimran-pabla]

Thanks @yushoyamaguchi for addressing these comments.

In other subcommands, variable name cmd is used. Can I ignore these warning messages, or should I change variable name to _ ?

It would be best if you fixed these comments ( these are static syntax checkers and have to make linters happy ).

Second, setting resolved tag for the place I fixed is my role or your role? (Currently, I only put 👍)
I'm sorry for ignorance about OSS development.

If you have addressed the comment; feel free to resolve it.

In addition, I replied to some your fix request comments which I cannot find the way to fix.

Please add a comment whichever comment is not clear, I will try my best to explain it further.

[harsimran-pabla]

General commit comment.

• Keep each commit about logical change instead of iterations on this PR.
• Add more details about the change in the commit description.

[yushoyamaguchi]

@asauber
Thank you for your reviewing.
I'll fix all improvement point, then tell you.

[harsimran-pabla]

Thanks @yushoyamaguchi, for bearing with me on this PR. There are a couple of things I would like to highlight: minor naming changes. And channel creations can be cleaned up. I'd suggest consolidating the channels, as shown in the example in one of the comments.

[yushoyamaguchi]

@harsimran-pabla

Thank you for kindly pointing out the places that needed improvement.
I'm happy because I could learn a lot.

I've fixed all the points you mentioned.

[harsimran-pabla]

Thanks, @yushoyamaguchi, for the change; it looks good. Please squash both commits into a single one.

[yushoyamaguchi]

@harsimran-pabla
Thank you so much for the detailed review
I've squashed.

[yushoyamaguchi]

@harsimran-pabla @asauber
Thank you for the approval.
Should I do something else for merging?
As I said in this PR, I want to add test scenario using this multicast subcommand after merging...

@fujitatomoya -san 's approval is required?
He said maybe not required but I can ask him if needed, because he is a my colleague.

[harsimran-pabla]

Thanks, @yushoyamaguchi. I think this PR is ready to merge; I believe all concerns are addressed. We can move forward with e2e testing independently.

[harsimran-pabla]

I'd suggest reaching out to @fujitatomoya to get his approval as well, since he reviewed this PR.

[yushoyamaguchi]

Thank you.

[fujitatomoya]

@harsimran-pabla @asauber thanks for the reviews, im good to go.

[yushoyamaguchi]

@harsimran-pabla @asauber @michi-covalent @fujitatomoya
Thank you so much!