CSPL-4125: Promote multi-platform images in release

[rlieberman-splunk]

Description

This PR promotes the multi-platform docker images during the release process. Starting in the 3.0.0 release, we build multi-platform images by default. During the release process, using docker pull, tag, and push would only pull the amd64 based manifest because that is the OS that the Github workflows are running on. These changes make sure that the multi-platform manifests get copied and promoted to all of the different repositories.

Example output using changes in this PR:

> docker buildx imagetools inspect rliebermansplunk/splunk-operator:3.0.0-RC-multiplatform
Name:      docker.io/rliebermansplunk/splunk-operator:3.0.0-RC-multiplatform
MediaType: application/vnd.oci.image.index.v1+json
Digest:    sha256:af031f0bc15c2e849c029098faee612aab4c6ae4fe031c0c054a9d5a0aef3b11
           
Manifests: 
  Name:        docker.io/rliebermansplunk/splunk-operator:3.0.0-RC-multiplatform@sha256:bc91aef04582ea974bfaa14d2d5af44fdbb018aa23f57863c796797d3088e091
  MediaType:   application/vnd.oci.image.manifest.v1+json
  Platform:    linux/amd64
               
  Name:        docker.io/rliebermansplunk/splunk-operator:3.0.0-RC-multiplatform@sha256:29940dd5fcb2d7f71da07d8f0ab72ae7997e638368026d079f0ab99b7ef6d166
  MediaType:   application/vnd.oci.image.manifest.v1+json
  Platform:    linux/arm64
               
  Name:        docker.io/rliebermansplunk/splunk-operator:3.0.0-RC-multiplatform@sha256:a2cb6eeb7d6b175db75622e5dded2c7ca0b6092f0ec7f3e112d7e6336ca4cd64
  MediaType:   application/vnd.oci.image.manifest.v1+json
  Platform:    unknown/unknown
  Annotations: 
    vnd.docker.reference.digest: sha256:bc91aef04582ea974bfaa14d2d5af44fdbb018aa23f57863c796797d3088e091
    vnd.docker.reference.type:   attestation-manifest
               
  Name:        docker.io/rliebermansplunk/splunk-operator:3.0.0-RC-multiplatform@sha256:efba0fe175f531264c7324582b9c66eb5fb80d9a412d6f8dd25b229eda2774e3
  MediaType:   application/vnd.oci.image.manifest.v1+json
  Platform:    unknown/unknown
  Annotations: 
    vnd.docker.reference.digest: sha256:29940dd5fcb2d7f71da07d8f0ab72ae7997e638368026d079f0ab99b7ef6d166
    vnd.docker.reference.type:   attestation-manifest

Example output of previous release:

> docker buildx imagetools inspect splunk/splunk-operator:3.0.0                 
Name:      docker.io/splunk/splunk-operator:3.0.0
MediaType: application/vnd.docker.distribution.manifest.v2+json
Digest:    sha256:ed02561995d46ff8eea143fa78f5da118ee6fdb500832e9a33b42d059a67e229

Key Changes

• Use regctl image copy to copy multi-platform rc images to dockerhub
• Use docker buildx imagetools create to tag multi-platform rc images in aws

Testing and Verification

• Both updated workflows were run from the branch: https://github.com/splunk/splunk-operator/actions/runs/19367051736

Related Issues

• https://splunk.atlassian.net/browse/CSPL-4125

PR Checklist

• Code changes adhere to the project's coding standards.
• Relevant unit and integration tests are included.
• Documentation has been updated accordingly.
• All tests pass locally.
• The PR description follows the project's guidelines.

[coveralls]

Pull Request Test Coverage Report for Build 19435104810

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 86.552%

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Totals
Change from base Build 19427516711:	0.02%
Covered Lines:	10710
Relevant Lines:	12374

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 19435104840

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 86.552%

---

Totals
Change from base Build 19427516711:	0.02%
Covered Lines:	10710
Relevant Lines:	12374

---

💛 - Coveralls