DLPX-91976 Step 4: linux-pkg: Prepare and update Ubuntu distribution pointer to new version

[palash-gandhi]

Problem

The linux-pkg repo contains pointers to focal which is the codename for Ubuntu 20.04. Now that we are starting with the Ubuntu LTS upgrade project, we need to move this pointer to noble which is the codename for Ubuntu 24.04. While we have not decided on the next LTS version (24.04 or 22.04) yet, this PR is part of a POC to decide on a version.
Also, the td-agent package was sourced from a focal-based source.

Solution

Update the pointer to noble and remove the hardcoded source of td-agent for now. I'll address it in a future PR when I run into an issue with that package.

Testing Done

To test this change, I created an upstreams/os-upgrade branch in the linux-kernel-generic repo from https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/noble and an os-upgrade branch from develop.

Next, I ran a check-updates job: http://ops.jenkins-palashgandhi.dcol2.delphix.com/job/linux-pkg/job/os-upgrade/job/check-updates/job/main/4/console with the following params:
LINUX_PKG_GIT_BRANCH =
DEVOPS_GATE_GIT_BRANCH = Branch of https://github.com/delphix/devops-gate/pull/3356
DCENTER_GROUP = bootstrap-24.04-poc (temporary buildserver created off of 24.04 in Step 1 of project)
DELPHIX_PACKAGE_MIRROR_MAIN = http://us-west-2.ec2.archive.ubuntu.com/ubuntu/

15:55:10  PACKAGE linux-kernel-generic: STAGE update_upstream STARTED
15:55:10  Running: update_upstream
15:55:10  Running: kernel_update_upstream generic
15:55:10  Running: cd /var/tmp/jenkins/workspace/linux-pkg/os-upgrade/check-updates/main/linux-pkg/packages/linux-kernel-generic/tmp/repo
15:55:10  Running: git checkout -q upstream-HEAD
15:55:38  Running: git remote add upstream https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/noble
15:55:38  Running: get_kernel_version_for_platform_from_apt generic
15:55:38  note: upstream tag prefix used: Ubuntu-6.8-6.8.0-41
15:55:38  tag with prefix Ubuntu-6.8-6.8.0-41 not found.
15:55:38  trying tag prefix: Ubuntu-6.8.0-41.
15:55:38  Running: git fetch upstream +refs/tags/Ubuntu-6.8.0-41.41:refs/tags/Ubuntu-6.8.0-41.41
15:56:48  From https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/noble