chore: Add CAPA jobs for v2.8.x release series

[nrb]

Add new jobs for the CAPA v2.8 release series.

Also remove unsupported and failing v2.6 series.

cc @damdo @AndiDog @dlipovetsky @richardcase

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: nrb

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[richardcase]

/lgtm

[damdo]

/lgtm

[k8s-ci-robot]

@nrb: Updated the job-config configmap in namespace default at cluster test-infra-trusted using the following files:

• key cluster-api-provider-aws-periodics-release-2.6.yaml using file ``
• key cluster-api-provider-aws-periodics-release-2.8.yaml using file config/jobs/kubernetes-sigs/cluster-api-provider-aws/cluster-api-provider-aws-periodics-release-2.8.yaml
• key cluster-api-provider-aws-presubmits-release-2.6.yaml using file ``
• key cluster-api-provider-aws-presubmits-release-2.8.yaml using file config/jobs/kubernetes-sigs/cluster-api-provider-aws/cluster-api-provider-aws-presubmits-release-2.8.yaml

In response to this:

Add new jobs for the CAPA v2.8 release series.

Also remove unsupported and failing v2.6 series.

cc @damdo @AndiDog @dlipovetsky @richardcase

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