Update init to not require rootfs=initramfs to use tmpfs

[anderbubble]

Description of the Pull Request (PR):

Using SELinux requires setting root=tmpfs; but the implementation of /init also required rootfstype=ramfs unnecessarily.

This fixes or addresses the following GitHub issues:

• Closes refactor wwinit/init script to resolve rootfs confusion #1093

Before submitting a PR, make sure you have done the following:

• Signed off on all commits (e.g., using git commit --signoff) in agreement to the DCO
• Read the documentation for contributing to Warewulf
• Added changes to the CHANGELOG if necessary
• Updated userdocs if necessary
• Based this PR against the appropriate branch (typically main)
• Added myself as a contributor to the Contributors File

[anderbubble]

@mslacken I tried this out and it appears to work for me, which leaves me confused why it was this way in the first place. Let me know if you have any concerns.

[anderbubble]

I don't know why yet, but ever since I made this change I get inconsistent behavior about init starting correctly. Until I can sort that out, I'm marking this a draft.

[anderbubble]

See also #822