feat(auth): support multiple accounts

[water-sucks]

Community Contribution License Agreement

By creating this pull request, I grant the project maintainers an unlimited,
perpetual license to use, modify, and redistribute these contributions under any terms they
choose, including both the AGPLv3 and the Fossorial Commercial license terms. I
represent that I have the right to grant this license for all contributed content.

Description

This adds support for multiple accounts, and does a bunch of refactoring to make this possible.

• Configuration files are now underneath $HOME/.config/pangolin, in a more standard location. In the future, this can use $XDG_CONFIG_HOME, if set.
• A new file, config.json, controls the log level, log path, and update checks. These can also be set through corresponding env vars, prefaced with PANGOLIN_CLI.
• A new file, accounts.json, is now being used for setting account information/other mutable state pertaining to them, such as the selected organization. All global viper state is banished!
• The API client and account store is now passed through a context.Context, inherited by the cobra.Command struct and passed to every function. The client is automatically instantiated with the active client's session token, if set.
• A new command, pangolin select account, can be used to switch the active account.

How to test?

• Login to a secondary account using pangolin auth login. You should see two accounts when selecting between them
• Select account using pangolin select account. If an OLM client is running, it should be shut down.
• Select accounts using the host's name as a filter. Host names should exactly match the queries; this can be facilitated using command-line completion in the future.

[miloschwartz]

Lgtm! Thanks @water-sucks