add slurm

[madhur-ob]

requires Netflix/metaflow#2134 to be merged first

Tested with the following flow with the Oleg2 stack:

from metaflow import FlowSpec, step, slurm, pypi, environment

class Movies(FlowSpec):

    @step
    def start(self):
        self.titles = ['Stranger Things', 'House of Cards', 'Game of Thrones']
        self.next(self.mid, foreach='titles')

    @environment(vars={
        "AWS_ACCESS_KEY_ID": "XXXX",
        "AWS_SECRET_ACCESS_KEY": "YYYY"
    })
    @slurm(
        username="ubuntu",
        address="18.236.81.10",
        ssh_key_file="~/Desktop/outerbounds/parallelcluster/madhur-slurm.pem",
    )
    @pypi(python='3.10.11', packages={'pandas': '2.1.1', 'numpy': '1.24.4', 'boto3': '1.35.40', 'requests': '2.32.3'})
    @step
    def mid(self):
        import pandas as pd

        self.series = pd.Series(['%s processed' % self.input])
        print(self.series)
        self.next(self.join)

    @pypi(python='3.10.11', packages={'pandas': '2.1.1', 'numpy': '1.24.4'})
    @step
    def join(self, inputs):
        import pandas as pd
        
        df = pd.DataFrame([inp.series for inp in inputs])
        df.columns = ["Value"]
        self.df = df.reset_index(drop=True)
        print(self.df)
        self.next(self.end)

    @step
    def end(self):
        print("Phew!")

if __name__ == '__main__':
    Movies()