[antlir2][chef_solo] aarch64 fbpkg handling

Summary:
fbpkg handling is a little wonky with chef-solo. chef ends up adding an
implicit `.aarch64` suffix, but then asks fbpkg to alias it with the old name.
It's all kind of a huge mess, but we can relatively easily support it by just
making a few refactors to use the correct chef library code and making some
tweaks to `fbpkg.fetch` to handle alternate calling conventions a little better.

Test Plan:
aarch64 works
```
❯ buck2 test -c fbcode.arch=aarch64 fbcode//antlir/antlir2/test_images/facebook/chef_solo/fbpkg:
Buck UI: https://www.internalfb.com/buck2/314630af-49a2-4f7d-9b0f-6739c6c1afa3
Test UI: https://www.internalfb.com/intern/testinfra/testrun/10696049118418788
Network: Up: 0B  Down: 0B
Jobs completed: 44. Time elapsed: 6.7s.
Tests finished: Pass 11. Fail 0. Fatal 0. Skip 0. Build failure 0
```

Didn't break x86_64
```
❯ buck2 test fbcode//antlir/antlir2/test_images/facebook/chef_solo/fbpkg:
Buck UI: https://www.internalfb.com/buck2/a51e38dc-19a1-4e9c-83ee-7b0d70f8c158
Test UI: https://www.internalfb.com/intern/testinfra/testrun/2533274994863480
Network: Up: 0B  Down: 0B
Jobs completed: 44. Time elapsed: 5.2s.
Tests finished: Pass 11. Fail 0. Fatal 0. Skip 0. Build failure 0
```

Reviewed By: sergeyfd

Differential Revision: D49506828

fbshipit-source-id: 40864951ca5511611bcdeef2c69b2ef693a3970f

antlir/antlir2/antlir2_compile/src/plan.rs

@@ -102,6 +102,7 @@ pub struct InstallFbpkg {
     pub tag: String,
     pub dst: Option<String>,
     pub organize: bool,
+    pub organize_alias: Option<String>,
 }
 
 #[derive(Debug, Clone, Deserialize, Serialize)]