updates Release Team README given recent cycle changes

[drewhagen]

What type of PR is this:

/kind documentation

What this PR does / why we need it:

Updates the Release Team README to improve accuracy and consistency with current release processes.

This PR addresses several areas where the documentation had become outdated:

Subteam mentions:

• Removes instances of "Release Notes", "Bug Triage", ect

Mermaid diagram improvements:

• Adds Production Readiness Review Freeze (PRR Freeze) to both release process diagrams
• Updates "CI Signal" to "Release Signal"
• Release Notes is now consolidated under Docs

These changes ensure the README accurately reflects the current Kubernetes release subteam processes and provides contributors with up-to-date examples and workflow diagrams.

cc: @kubernetes/sig-release-leads @kubernetes/release-team

Which issue(s) this PR fixes:

None

Special notes for your reviewer:

The Mermaid diagram changes specifically address the new Production Readiness Review Freeze milestone and subteam consolidations.

[tico88612]

It's good from the Release Signal.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: drewhagen, tico88612

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

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Needs approval from an approver in each of these files:

• release-team/OWNERS [drewhagen]

Approvers can indicate their approval by writing /approve in a comment
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[tico88612]

/remove-lgtm

EDIT: I thought approve wouldn't give LGTM, but I think the rest is fine.

[tico88612]

Wait, I thought approve wouldn't give LGTM, that's my mistake. :(

[drewhagen]

@tico88612 lol, this is the same thing I did on the PR! 😂