Autobuild overlays option won't build combined runtime/system overlays

[Prepultrue]

Steps to reproduce

Remove the existing overlay image so autobuild should rebuild it

rm -f /var/lib/warewulf/provision/overlays/n001/__RUNTIME__.img{,.gz}

Request the runtime overlay image:

# curl -v --local-port 500-1000 'http://WW_HOST:9873/provision/00:11:22:33:44:55?stage=runtime'
*   Trying WW_HOST...
* TCP_NODELAY set
* Local port: 500
* Connected to WW_HOST (WW_HOST) port 9873 (#0)
> GET /provision/00:11:22:33:44:55?stage=runtime HTTP/1.1
> Host: WW_HOST:9873
> User-Agent: curl/7.61.1
> Accept: */*
> 
< HTTP/1.1 404 Not Found
< Date: Wed, 08 May 2024 03:15:47 GMT
< Content-Length: 0
< 
* Connection #0 to host WW_HOST left intact

Error message

[Wed May  8 13:17:27 AEST 2024] RECV   : hwaddr: 00:11:22:33:44:55, ipaddr: WW_HOST:500, stage: runtime
[Wed May  8 13:17:27 AEST 2024] SERV   : stage_file '/var/lib/warewulf/provision/overlays/n001/__RUNTIME__.img'
[Wed May  8 13:17:27 AEST 2024] ERROR  : Not found: /var/lib/warewulf/provision/overlays/n001/__RUNTIME__.img

Information on your system

# wwctl version 
wwctl version:	4.5.1-1
rpc version: apiPrefix:"rc1"  apiVersion:"1"  warewulfVersion:"4.5.1-1"

# cat /etc/os-release 
NAME="Rocky Linux"
VERSION="8.9 (Green Obsidian)"
ID="rocky"
ID_LIKE="rhel centos fedora"
VERSION_ID="8.9"
PLATFORM_ID="platform:el8"
PRETTY_NAME="Rocky Linux 8.9 (Green Obsidian)"
ANSI_COLOR="0;32"
LOGO="fedora-logo-icon"
CPE_NAME="cpe:/o:rocky:rocky:8:GA"
HOME_URL="https://rockylinux.org/"
BUG_REPORT_URL="https://bugs.rockylinux.org/"
SUPPORT_END="2029-05-31"
ROCKY_SUPPORT_PRODUCT="Rocky-Linux-8"
ROCKY_SUPPORT_PRODUCT_VERSION="8.9"
REDHAT_SUPPORT_PRODUCT="Rocky Linux"
REDHAT_SUPPORT_PRODUCT_VERSION="8.9"

# grep -B3 autobuild /etc/warewulf/warewulf.conf
warewulf:
  port: 9873
  secure: true
  autobuild overlays: true

General information

• I have run wwctl version and reported the contents of /etc/os-release
• I have searched the issues of this repo and believe this is not a duplicate
• I have captured and reported relevant error messages and logs

[Prepultrue]

This seems to be because:

• getOverlayFile will only every be called with either context or request_overlays/stage_overlays set
• overlay.BuildOverlay immediately bails out when no overlayNames are supplied

[griznog]

More motivation for #1018 ?