Remove all absolute paths in the Auto3DSeg templates generation (BundleGen) process

[mingxin-zheng]

Describe the bug

The absolute paths in the Auto3DSeg BundleGen are blocking users to customize and use bundles locally.

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Install '....'
3. Run commands '....'

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
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Environment

Ensuring you use the relevant python executable, please paste the output of:

python -c "import monai; monai.config.print_debug_info()"

Additional context
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[vikashg]

@mingxin-zheng we can close this after the PR is approved