chore: Replace Requests with PodGroupRequests

[tenzen-y]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

As we discussed in #4355 (comment), we clarified the expected requests. The current Requests evokes Pod requests, but actually, it will be a group of Pod requests.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: tenzen-y

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [tenzen-y]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[netlify]

✅ Deploy Preview for kubernetes-sigs-kueue canceled.

Name	Link
🔨 Latest commit	09ed96a
🔍 Latest deploy log	https://app.netlify.com/sites/kubernetes-sigs-kueue/deploys/67c0b60fcd4df40008adae85

[tenzen-y]

/assign @mimowo

[mimowo]

/hold
I'm not convinced this is the right direction. In the comment #4355 (comment) I meant specifically the context of CountIn, but I think the new name is not that good for other contexts.

For example, the type is also used to represent capacity. I think calling it PodGroupRequests it even more confusing in that context. And longer.

Thinking more about the capacity case Requests is misleading too - maybe just call it Resources or ResourcesMap.
Then, depending on the context we could:

• have better function comments clarifying the role
• have contextual aliases like PodGroupRequests of Capacity, but I'm not sure if the aliases simplify it