llama-2 presets: Add dockerignore file (#765)

This commit adds a dockerignore file for the llama-2 preset. This change
will ignore copying the `.git` folder while building the docker image.

**Reason for Change**:

This change was added to reduce the model image size by ignoring the
`.git` folder while building the docker image.

Before this change:

```console
$ docker images
REPOSITORY                TAG          IMAGE ID       CREATED        SIZE
meta-llama/llama-2-70b    1cb3547      4715d3ed9f6b   10 hours ago   289GB
```

After this change:

```console
$ docker images
REPOSITORY                TAG          IMAGE ID       CREATED        SIZE
meta-llama/llama-2-70b    1cb3547      6527d68eae17   2 days ago     151GB
```

52% reduction in image size for this model. And for any repository that
is mature enough with model updates the size reduction difference will
be more.

**Issue Fixed**:

Partially fixes #764. Partially because it is not fixing all the models
out there. Just for this one llama2.

Signed-off-by: Suraj Deshmukh <[email protected]>

docker/presets/models/llama-2/Dockerfile.dockerignore

@@ -0,0 +1 @@
+**/.git