Add --jobs 0 for git submodule update (#61311)

Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61311

Pull Request resolved: https://github.com/pytorch/pytorch/pull/61152

Some related docs about `submodule.fetchJobs`
https://git-scm.com/docs/git-config#Documentation/git-config.txt-submodulefetchJobs

```
time git submodule update --init --recursive
________________________________________________________
Executed in  243.20 secs    fish           external
   usr time   49.64 secs  213.00 micros   49.64 secs
   sys time   29.27 secs  795.00 micros   29.27 secs
```

```
time git submodule update --init --recursive --jobs 4
________________________________________________________
Executed in  143.04 secs    fish           external
   usr time   51.06 secs  246.00 micros   51.06 secs
   sys time   30.96 secs  742.00 micros   30.96 secs
```

```
time git submodule update --init --recursive --jobs 8
________________________________________________________
Executed in  124.64 secs    fish           external
   usr time   51.76 secs  264.00 micros   51.76 secs
   sys time   30.49 secs  739.00 micros   30.49 secs

```

```
time git submodule update --init --recursive --jobs 0 # use all online cpus
 ________________________________________________________
Executed in  129.75 secs    fish           external
   usr time   51.64 secs  181.00 micros   51.64 secs
   sys time   31.49 secs  781.00 micros   31.49 secs

```

Test Plan: Imported from OSS

Reviewed By: 1ntEgr8

Differential Revision: D29560875

Pulled By: zhouzhuojie

fbshipit-source-id: 556027dffe744c66428075a8a1bf64683930aaaf

Dockerfile

@@ -38,7 +38,7 @@ RUN curl -fsSL -v -o ~/miniconda.sh -O  https://repo.anaconda.com/miniconda/Mini
 FROM dev-base as submodule-update
 WORKDIR /opt/pytorch
 COPY . .
-RUN git submodule update --init --recursive
+RUN git submodule update --init --recursive --jobs 0
 
 FROM conda as build
 WORKDIR /opt/pytorch