Leading slashes in container ignorefile don't match as expected

[foriequal0]

Issue Description

I noticed that podman build on Windows takes a huge amount of time to prepare just the context.
It turned out that my Containerignore file didn't work at all.
Huge git repository and build cache are included in the build context.
Removing leading slashes fixed the problem.

Steps to reproduce the issue

Steps to reproduce the issue

1. Use forward slash in ignorefile
   I had ignorefile like this

/.git/
/target/

2. Build

Describe the results you received

It takes a long time to prepare the context when the context is huge

Describe the results you expected

It shouldn't take a long time to prepare

podman info output

host:
  arch: amd64
  buildahVersion: 1.38.0
  cgroupControllers:
  - cpuset
  - cpu
  - cpuacct
  - blkio
  - memory
  - devices
  - freezer
  - net_cls
  - perf_event
  - net_prio
  - hugetlb
  - pids
  - rdma
  - misc
  cgroupManager: cgroupfs
  cgroupVersion: v1
  conmon:
    package: conmon-2.1.12-2.fc40.x86_64
    path: /usr/bin/conmon
    version: 'conmon version 2.1.12, commit: '
  cpuUtilization:
    idlePercent: 99.34
    systemPercent: 0.18
    userPercent: 0.48
  cpus: 16
  databaseBackend: sqlite
  distribution:
    distribution: fedora
    variant: container
    version: "40"
  eventLogger: journald
  freeLocks: 2025
  hostname: sclee-PC
  idMappings:
    gidmap: null
    uidmap: null
  kernel: 5.15.167.4-microsoft-standard-WSL2
  linkmode: dynamic
  logDriver: journald
  memFree: 29683224576
  memTotal: 33573638144
  networkBackend: netavark
  networkBackendInfo:
    backend: netavark
    dns:
      package: aardvark-dns-1.13.1-1.fc40.x86_64
      path: /usr/libexec/podman/aardvark-dns
      version: aardvark-dns 1.13.1
    package: netavark-1.13.1-1.fc40.x86_64
    path: /usr/libexec/podman/netavark
    version: netavark 1.13.1
  ociRuntime:
    name: crun
    package: crun-1.19.1-1.fc40.x86_64
    path: /usr/bin/crun
    version: |-
      crun version 1.19.1
      commit: 3e32a70c93f5aa5fea69b50256cca7fd4aa23c80
      rundir: /run/crun
      spec: 1.0.0
      +SYSTEMD +SELINUX +APPARMOR +CAP +SECCOMP +EBPF +CRIU +LIBKRUN +WASM:wasmedge +YAJL
  os: linux
  pasta:
    executable: /usr/bin/pasta
    package: passt-0^20241211.g09478d5-1.fc40.x86_64
    version: |
      pasta 0^20241211.g09478d5-1.fc40.x86_64
      Copyright Red Hat
      GNU General Public License, version 2 or later
        <https://www.gnu.org/licenses/old-licenses/gpl-2.0.html>
      This is free software: you are free to change and redistribute it.
      There is NO WARRANTY, to the extent permitted by law.
  remoteSocket:
    exists: true
    path: unix:///run/podman/podman.sock
  rootlessNetworkCmd: pasta
  security:
    apparmorEnabled: false
    capabilities: CAP_CHOWN,CAP_DAC_OVERRIDE,CAP_FOWNER,CAP_FSETID,CAP_KILL,CAP_NET_BIND_SERVICE,CAP_SETFCAP,CAP_SETGID,CAP_SETPCAP,CAP_SETUID,CAP_SYS_CHROOT
    rootless: false
    seccompEnabled: true
    seccompProfilePath: /usr/share/containers/seccomp.json
    selinuxEnabled: false
  serviceIsRemote: true
  slirp4netns:
    executable: ""
    package: ""
    version: ""
  swapFree: 8578301952
  swapTotal: 8589934592
  uptime: 138h 54m 20.00s (Approximately 5.75 days)
  variant: ""
plugins:
  authorization: null
  log:
  - k8s-file
  - none
  - passthrough
  - journald
  network:
  - bridge
  - macvlan
  - ipvlan
  volume:
  - local
registries:
  search:
  - docker.io
store:
  configFile: /usr/share/containers/storage.conf
  containerStore:
    number: 1
    paused: 0
    running: 0
    stopped: 1
  graphDriverName: overlay
  graphOptions:
    overlay.imagestore: /usr/lib/containers/storage
    overlay.mountopt: nodev,metacopy=on
  graphRoot: /var/lib/containers/storage
  graphRootAllocated: 1081101176832
  graphRootUsed: 101926649856
  graphStatus:
    Backing Filesystem: extfs
    Native Overlay Diff: "false"
    Supports d_type: "true"
    Supports shifting: "false"
    Supports volatile: "true"
    Using metacopy: "true"
  imageCopyTmpDir: /var/tmp
  imageStore:
    number: 29
  runRoot: /run/containers/storage
  transientStore: false
  volumePath: /var/lib/containers/storage/volumes
version:
  APIVersion: 5.3.1
  Built: 1732147200
  BuiltTime: Thu Nov 21 09:00:00 2024
  GitCommit: ""
  GoVersion: go1.22.7
  Os: linux
  OsArch: linux/amd64
  Version: 5.3.1

Podman in a container

No

Privileged Or Rootless

Rootless

Upstream Latest Release

Yes

Additional environment details

Windows 11

Additional information

https://docs.docker.com/build/concepts/context/#syntax
leading and trailing slashes should be ignored as per Dockerignore spec