Support branch for cm pull repo

[arjunsuresh]

Currently the behaviour of --branch with cm pull repo command is not as expected. Instead of cloning from the given branch, cm is currently cloning from the default branch

arjunsuresh@Arjuns-MacBook-Pro ~ % cm pull repo mlcommons@cm4mlops --branch=mlperf-inference
=======================================================
Alias:    mlcommons@cm4mlops
URL:      https://github.com/mlcommons/cm4mlops
Branch:   mlperf-inference
Checkout:

Local path: /Users/arjunsuresh/CM/repos/mlcommons@cm4mlops

git clone https://github.com/mlcommons/cm4mlops mlcommons@cm4mlops

Cloning into 'mlcommons@cm4mlops'...
remote: Enumerating objects: 63643, done.
remote: Counting objects: 100% (12668/12668), done.
remote: Compressing objects: 100% (1123/1123), done.
remote: Total 63643 (delta 11708), reused 11575 (delta 11545), pack-reused 50975
Receiving objects: 100% (63643/63643), 27.32 MiB | 20.75 MiB/s, done.
Resolving deltas: 100% (45475/45475), done.

git checkout -b mlperf-inference

Switched to a new branch 'mlperf-inference'

CM alias for this repository: mlcommons@cm4mlops

Reindexing all CM artifacts. Can take some time ...
Took 0.6 sec.

Now,

cd $HOME/CM/repos/mlcommons@cm4mlops
git log

gives

commit d5fcf382064bad45acb63ca7201171d384942541 (HEAD -> mlperf-inference, origin/main, origin/HEAD, main)

Also, repeating the command throws an error.

arjunsuresh@Arjuns-MacBook-Pro mlcommons@cm4mlops % cm pull repo mlcommons@cm4mlops --branch=mlperf-inference
=======================================================
Alias:    mlcommons@cm4mlops
URL:      https://github.com/mlcommons/cm4mlops
Branch:   mlperf-inference
Checkout:

Local path: /Users/arjunsuresh/CM/repos/mlcommons@cm4mlops

git pull

There is no tracking information for the current branch.
Please specify which branch you want to merge with.
See git-pull(1) for details.

    git pull <remote> <branch>

If you wish to set tracking information for this branch you can do so with:

    git branch --set-upstream-to=origin/<branch> mlperf-inference


git checkout -b mlperf-inference

fatal: a branch named 'mlperf-inference' already exists

CM error: git checkout for repository failed!