Allow wildcards in localSchemaFile in service:push

Hi. In the command `apollo service:push` the `--localSchemaFile` flag currently has syntax to specify multiple files like so:

```
--localSchemaFile=src/app/graphql/schema/schema1.gql,src/app/graphql/schema/schema2.gql
```

it would be great to have a way to specify wildcards or glob patterns so that you don't have to include each and every file while specifying the path like this:

```
--localSchemaFile=src/app/graphql/schema/*.gql
```

Thanks.

Start at the service:push entry point and trace how the --localSchemaFile value is parsed, including its existing comma-separated file syntax. Done means wildcard or glob patterns are accepted for schema files while the current multiple-file form continues to work; inspect the relevant tests, if present, to verify both forms.

Written by the indexing model from the issue text.