bpftrace: Rename *.8 to *.bt.8 to avoid bcc conflicts
bpftrace: Rename *.8 to *.bt.8 to avoid bcc conflicts

bpftrace ships *.bt replacement scripts for the original bcc programs
but still installs their manual pages as *.8 rather than *.bt.8 which
conflicts with the original manual pages.

Rename them to recover the original manuals and avoid conflict spam:
```
building '/nix/store/jspx13hyfi2m9vlnbj5iywk6rxpxp7y0-system-path.drv'...
warning: collision between `/nix/store/dv7x07rmd2m7596f38kl9d5bnv545qz7-bpftrace-0.14.1-man/share/man/man8/biolatency.8.gz' and `/nix/store/lw1kw7077wk3j6cnvjrm904rs2w7785p-bcc-0.24.0/share/man/man8/biolatency.8.gz'
[... 28 more duplicate manuals ...]
```

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