Executor always creates a Python 3.8 execution environment

We currently [hardcode version 3.8](https://github.com/AgnostiqHQ/covalent-awslambda-plugin/blob/c412d82ca8b54d2f685a95198a6e2be8e7bd2f76/covalent_awslambda_plugin/awslambda.py#L272) for the Lambda python version. This could cause problems on other versions of Python that we support since Cloudpickle only guarantees protocol compatibility within a python minor version.

Start at covalent_awslambda_plugin/awslambda.py around line 272, where the Lambda Python version is hardcoded to 3.8. Trace how the executor selects its runtime and determine how the supported Python minor version should be represented. Done means the Lambda environment matches the execution Python version and maintains Cloudpickle protocol compatibility.

Written by the indexing model from the issue text.