feat(ubuntu): add Ubuntu 26.04 LTS (Resolute Raccoon) support (#512)

* feat(ubuntu): add Ubuntu 26.04 (Plucky Puffin) support

- Fix hardcoded dist in ubuntu provider's loadRepoConfig() to accept
  dist as a parameter, matching azl/emt/rcd provider patterns
- Create config/osv/ubuntu/ubuntu26/ directory tree with config.yml,
  chrootenv configs, provider repo configs (plucky codename), default
  image configs, and additional files
- Add ubuntu26 to dist enum in os-config.schema.json
- Add ubuntu OS->dist constraint (ubuntu24, ubuntu26) in
  os-image-template.schema.json
- Add ubuntu entries to GetProviderName() and GetDistroVersion() maps
  in config.go
- Add ubuntu26-x86_64-minimal-raw.yml example image template
- Add ubuntu26 test cases for provider init, name, and repo config
- Add ubuntu24/ubuntu26 to TestAllSupportedProviders config test
- Update README.md, release-notes.md, and templates documentation

* fix(ubuntu): use resolute codename for Ubuntu 26.04 LTS

Replace plucky (25.04) codename references with resolute (26.04 LTS)
across all ubuntu26 config files:
- Update repo configs (repo.yml, amd64_repo.yml, arm64_repo.yml)
- Rename ubuntu-plucky.list to ubuntu-resolute.list
- Update all default image configs referencing the sources list
- Fix release-notes.md codename (Resolute Rattlesnake, not Plucky Puffin)

Addresses Copilot review comments on PR #512.

* chore: auto-update coverage threshold to 66.3% (was 66.2%)

* docs: revert release-notes.md Will add later for future release update

---------

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: arodage

.coverage-threshold

@@ -1 +1 @@
-66.2
+66.3

README.md

@@ -20,6 +20,7 @@ combinations. The table below lists the OS and architecture combinations that ar
 | Red Hat Compatible Distro | rcd10 | x86_64 |
 | Wind River eLxr | elxr12 | x86_64 |
 | Ubuntu | ubuntu24 | x86_64 |
+| Ubuntu | ubuntu26 | x86_64 |
 
 ## Quick Start
 

config/osv/ubuntu/ubuntu26/chrootenvconfigs/chrootenv_aarch64.yml

@@ -0,0 +1,30 @@
+essential:
+  - dpkg
+  - apt
+  - debianutils
+  - init-system-helpers
+  - dash
+  - mount
+  - sysvinit-utils
+  - gzip
+  - bash
+  - util-linux
+  - tar
+  - base-files
+  - base-passwd
+  - sed
+  - bsdutils
+  - coreutils
+  - findutils
+  - grep
+  - login
+  - perl-base
+  - diffutils
+  - libc-bin
+  - hostname
+  - ncurses-bin
+  - ncurses-base
+
+packages:
+  - mmdebstrap
+  - grub-efi-arm64-bin

config/osv/ubuntu/ubuntu26/chrootenvconfigs/chrootenv_x86_64.yml

@@ -0,0 +1,31 @@
+essential:
+  - dpkg
+  - apt
+  - debianutils
+  - init-system-helpers
+  - dash
+  - mount
+  - sysvinit-utils
+  - gzip
+  - bash
+  - util-linux
+  - tar
+  - base-files
+  - base-passwd
+  - sed
+  - bsdutils
+  - coreutils
+  - findutils
+  - grep
+  - login
+  - perl-base
+  - diffutils
+  - libc-bin
+  - hostname
+  - ncurses-bin
+  - ncurses-base
+
+packages:
+  - mmdebstrap
+  - grub-pc-bin
+  - grub-efi-amd64-bin

config/osv/ubuntu/ubuntu26/chrootenvconfigs/local.list

@@ -0,0 +1 @@
+deb [trusted=yes] file:///cdrom/cache-repo stable main

config/osv/ubuntu/ubuntu26/config.yml

@@ -0,0 +1,15 @@
+# Canonical Ubuntu 26.04 LTS OS Configuration
+# This file defines architecture-specific build configurations for Canonical Ubuntu 26.04 LTS
+
+x86_64:
+  dist: ubuntu26                                    # Distribution identifier
+  arch: x86_64                                      # Target architecture
+  pkgType: deb                                      # Package management system
+  chrootenvConfigFile: chrootenvconfigs/chrootenv_x86_64.yml  # Path to chrootenv config
+  releaseVersion: "26.04"                           # Distribution release version
+aarch64:
+  dist: ubuntu26                                    # Distribution identifier
+  arch: aarch64                                      # Target architecture
+  pkgType: deb                                      # Package management system
+  chrootenvConfigFile: chrootenvconfigs/chrootenv_aarch64.yml  # Path to chrootenv config
+  releaseVersion: "26.04"                           # Distribution release version

config/osv/ubuntu/ubuntu26/imageconfigs/additionalfiles/dhcp.network

@@ -0,0 +1,10 @@
+[Match]
+Name=en*
+
+[Network]
+DHCP=yes
+IPv6AcceptRA=no
+
+[DHCPv4]
+SendRelease=false
+ClientIdentifier=mac

config/osv/ubuntu/ubuntu26/imageconfigs/additionalfiles/getty@.service

@@ -0,0 +1,7 @@
+[Service]
+ExecStart=
+ExecStart=-/sbin/agetty --noclear --autologin root --keep-baud %I $TERM
+
+# Default to tty1 but allow other choices
+[Install]
+Alias=getty.target.wants/getty@tty1.service

config/osv/ubuntu/ubuntu26/imageconfigs/additionalfiles/serial-getty@.service

@@ -0,0 +1,7 @@
+[Service]
+ExecStart=
+ExecStart=-/sbin/agetty --noclear --autologin root --keep-baud %I $TERM
+
+# Default to ttyS0 but allow other choices
+[Install]
+Alias=getty.target.wants/serial-getty@ttyS0.service

config/osv/ubuntu/ubuntu26/imageconfigs/additionalfiles/ubuntu-resolute.list

@@ -0,0 +1,3 @@
+deb http://archive.ubuntu.com/ubuntu resolute main restricted universe multiverse
+deb http://archive.ubuntu.com/ubuntu resolute-updates main restricted universe multiverse
+deb http://archive.ubuntu.com/ubuntu resolute-security main restricted universe multiverse