[Runtimes] Adding a modifier and auto-mount option to configure multiple env variables

[theSaarco]

Added a modifier function set_env_variables to add multiple env. variables to a runtime. Also added an env auto-mount option to use this function automatically. This can be used to mount an arbitrary set of env variables to every runtime in a project.
While there are existing ways through MLRun/KFP-modifiers to add env. variables to runtimes, they have some short-comings, which this function solves:

• Since it's a modifier, it can be used with RunConfig which has an option to apply modifiers, but does not have ways to set env. variables on the RunConfig itself. Also, since auto-mount option is available, it can be used for every job submitted without having to tweak the RunConfig parameters
• It accepts multiple env. variables in a single execution. This makes it flexible and suitable to use in auto-mount where there's a single default modifier which can be configured
• The variables can be passed as a dictionary or as kwargs. Again, this makes it easier to configure it as auto-mount function. For example, you can call:
  function.apply(set_env_variables({"ENV1": "value1", "ENV2": "value2"}))
  and can also do the same with:
  function.apply(set_env_variables(ENV1="value1", ENV2="value2"))
  The kwargs option is more limited and should be used for simple keys/values, while the dictionary option can be used for keys which do not pass as Python parameter names etc.