Read Coffea config from TOML file

[JayjeetAtGithub]

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[JayjeetAtGithub]

@oshadura Here I have created a concept PR to create a global coffea config file which contains skyhook parameters. The coffea config file is located in the $HOME/.coffea.toml. We read this config file inside the Runner and read out skyhook config out of it. The user just needs to define use_skyhook=True now. Please let me know if this is in the right direction to make Coffea/Skyhook user-friendly.

[lgray]

Please do not make this configuration information for skyhook a requirement for every single executor. That's a big change for our users.

[JayjeetAtGithub]

@lgray Thanks a lot for looking into this. For the very same reason, I have kept the .coffea.toml file as optional. If there exists a .coffea.toml, then it will be read, otherwise it is not required. This config file currently serves only skyhook specific config, but serves as a placeholder to add other backend specific config in the future.

[lgray]

@JayjeetAtGithub are you done with this PR?

[JayjeetAtGithub]

@lgray Yes, I am done