Toolbx set KCM credential cache by default

**Describe the bug**
By default, toolbx create a file /etc/krb5.conf.d/kcm_default_ccache with the following content:
```
# Written by Toolbx
# https://containertoolbx.org/
#
# # To disable the KCM credential cache, comment out the following lines.

[libdefaults]
default_ccache_name = KCM:
```

If you use toolbx to get a Fedora system without setting `sssd-kcm` outside the container, kinit fail with a error:
```
kinit: Connection refused while getting default ccache
```
See https://discussion.fedoraproject.org/t/kinit-connection-refused-while-getting-default-ccache/136323

Debugging show that kinit try to connect to a socket that is absent in /var/tmp, and so fail.

It seems that the function configureKerberos ( see https://github.com/containers/toolbox/blob/431f7f07c744e9243fb94c289be75e05c31ee1b2/src/cmd/initContainer.go#L543C6-L543C23 ) is unconditionally called and will always create the configuration because `/etc/krb5.conf` always exist on Fedora since it get created as soon as `krb5-libs` is installed, and this is pulled by `openssh-clients`, installed by default, see:

```
[misc@toolbx ~]$ rpm -qf /etc/krb5.conf
krb5-libs-1.21.3-6.fc42.x86_64

[misc@toolbx ~]$ LC_ALL=C rpm -e --test krb5-libs-1.21.3-6.fc42.x86_64
error: Failed dependencies:
libgssapi_krb5.so.2()(64bit) is needed by (installed) libtirpc-1.3.6-1.rc3.fc42.2.x86_64
libgssapi_krb5.so.2()(64bit) is needed by (installed) libssh-0.11.2-1.fc42.x86_64
libgssapi_krb5.so.2()(64bit) is needed by (installed) libcurl-8.11.1-5.fc42.x86_64
libgssapi_krb5.so.2()(64bit) is needed by (installed) openssh-clients-9.9p1-11.fc42.x86_64
libgssapi_krb5.so.2(gssapi_krb5_2_MIT)(64bit) is needed by (installed) libtirpc-1.3.6-1.rc3.fc42.2.x86_64
libgssapi_krb5.so.2(gssapi_krb5_2_MIT)(64bit) is needed by (installed) libssh-0.11.2-1.fc42.x86_64
libgssapi_krb5.so.2(gssapi_krb5_2_MIT)(64bit) is needed by (installed) libcurl-8.11.1-5.fc42.x86_64
libgssapi_krb5.so.2(gssapi_krb5_2_MIT)(64bit) is needed by (installed) openssh-clients-9.9p1-11.fc42.x86_64
libk5crypto.so.3()(64bit) is needed by (installed) libtirpc-1.3.6-1.rc3.fc42.2.x86_64
libkrb5.so.3()(64bit) is needed by (installed) libtirpc-1.3.6-1.rc3.fc42.2.x86_64
```

And while sssd-kcm is installed on my Fedora system, it doesn't start because it can't read its configuration (which I didn't need to until now). So this could have been working fine in the past, but failed due to a change in `sssd`.

So I think that `toolbx` shouldn't rely on `sssd-kcm` to be running without checking that first, as it could be used where it is not setup (eg, a non Fedora distro, or my installation ).

**Steps how to reproduce the behaviour**
1. Run `toolbox create test -d fedora -r 42`
2. Run `toolbox enter test`
3. Run `sudo dnf install fedora-packager-kerberos`
4. Run `klist`
5. See error

**Expected behaviour**
Klist (or kinit or anything) should work and not stop with a error on the cache.

**Actual behaviour**
klist (or kinit, or others) show a error:
```
kinit: Connection refused while getting default ccache
```

**Output of `toolbox --version` (v0.0.90+)**
```
$ toolbox --version
toolbox version 0.2
```
**Toolbx package info (`rpm -q toolbox`)**
```
$ rpm -q toolbox
toolbox-0.2-1.fc42.x86_64
```

**Output of `podman version`**
e.g.,
```
Client: Podman Engine
Version: 5.5.2
API Version: 5.5.2
Go Version: go1.24.4
Git Commit: e7d8226745ba07a64b7176a7f128e4ef53225a0e
Built: Tue Jun 24 02:00:00 2025
Build Origin: Fedora Project
OS/Arch: linux/amd64
```

**Podman package info (`rpm -q podman`)**
`podman-5.5.2-1.fc42.x86_64`

**Info about your OS**
A bootc image of Fedora silverblue 42. If this matter, the Dockerfile is here: https://github.com/mscherer/custom_silverblue/blob/main/Dockerfile but besides adding and removeing package, I do not think I have made anythink that would impact this problem.

Start in src/cmd/initContainer.go at configureKerberos, then reproduce the issue with the Fedora 42 toolbox create, enter, fedora-packager-kerberos, and klist steps. Determine how the KCM configuration is created when sssd-kcm is not usable; done means klist and kinit no longer fail with a refused KCM cache in that container scenario.

Written by the indexing model from the issue text.