add dotgit command

[MaineK00n]

add utility command for vuls-data-* .git operation

// vuls-data-update dotgit list
$ vuls-data-update dotgit list
...
vuls-data-raw-redhat-vex
...
vuls-data-extracted-redhat-vex
...

// vuls-data-update dotgit pull <data source>
$ vuls-data-update dotgit pull vuls-data-raw-redhat-vex

// vuls-data-update dotgit merge <current> [<archive>]
$ vuls-data-update dotgit merge vuls-data-raw-redhat-vex vuls-data-raw-redhat-vex-archive-2 vuls-data-raw-redhat-vex-archive-1

// vuls-data-update dotgit contains <datasource> <commit hash>
$ vuls-data-update dotgit contains vuls-data-raw-redhat-vex 012abc

// vuls-data-update dotgit cat <data source> <branch|commit hash> <filepath>
$ vuls-data-update dotgit cat vuls-data-raw-redhat-vex 2025/CVE-2025-0001.json

// vuls-data-update dotgit find <data source> <branch|commit hash> <word>
$ vuls-data-update dotgit find vuls-data-raw-redhat-vex

// vuls-data-update dotgit grep <data source> <branch|commit hash> <word>
$ vuls-data-update dotgit grep vuls-data-raw-redhat-vex

---
// vuls-data-update dotgit diff <data source> <filepath> <branch|commit hash> <branch|commit hash>
// vuls-data-update dotgit compress