Make optional deps really optional (#1738)

This assigns groups to netifaces and android_backup dependencies so that
they shouldn't be required for building the package (e.g. by installing
the git checkout using pip). `PKG-INFO` looks now like this for these deps:
```
Requires-Dist: android_backup (>=0,<1); extra == "backup_extraction"
Requires-Dist: netifaces (>=0,<1); extra == "updater"
```

pyproject.toml

@@ -52,6 +52,8 @@ PyYAML = ">=5,<7"
 
 [tool.poetry.extras]
 docs = ["sphinx", "sphinx_click", "sphinxcontrib-apidoc", "sphinx_rtd_theme", "myst-parser"]
+updater = ["netifaces"]
+backup_extract = ["android_backup"]
 
 [tool.poetry.dev-dependencies]
 pytest = ">=6.2.5"