fix/feat: add cfg module to get or create the .wash directory

[ghost]

Fixes #215.

Currently if the .wash folder does not already exist, the ctx commands fail. This PR adds a cfg module along with a cfg_dir function that gets the .wash directory, and creates it if it does not exist.

This will need to be added to all of the functions that use the .wash directory. That looks like keys.rs and a few other ones in ctx. I'll implement these after getting a review on this design and any feedback you guys have.

[ghost]

Follow up question @brooksmtownsend - Why do we have separate environment variables for each part of the config directory? Like WASH_CONTEXTS etc. Could we just have a WASH_CONFIG variable so they can customize where the config is stored, but not the layout inside the config folder?

My thinking is that if we then add more configuration options, users would have to maintain tons of environment variables if they wanted to customize where the config is stored, vs just setting a single one and calling it a day.

[brooksmtownsend]

Why do we have separate environment variables for each part of the config directory? Like WASH_CONTEXTS etc. Could we just have a WASH_CONFIG variable so they can customize where the config is stored, but not the layout inside the config folder?

The main reason here was that someone could feasibly set WASH_KEYS=/tmp/mykeys where they mounted a folder containing keys, and it wouldn't have to be called /path/to/folder/keys.

I think there's three possible scenarios for someone configuring wash

1. User is fine with just using $HOME/.wash, no configuration needed (most common)
2. User wants to use a custom directory for wash things, e.g. $HOME/github/wash_cfg/, in which case a WASH_CONFIG or WASH_CFG_DIR environment variable is best
3. User wants to individually use a custom directory, e.g. a filesystem mounted folder, for keys or contexts like /home/washctxs

We currently support all three options with WASH_KEYS and WASH_CONTEXTS, and if we used a WASH_CFG_DIR variable we couldn't support option 3. For now I lean towards keeping _KEYS and _CONTEXTS even though it's a little more verbose just because it's more configurable, but I'm certainly be open to more discussion

[ghost]

We currently support all three options with WASH_KEYS and WASH_CONTEXTS, and if we used a WASH_CFG_DIR variable we couldn't support option 3. For now I lean towards keeping _KEYS and _CONTEXTS even though it's a little more verbose just because it's more configurable, but I'm certainly be open to more discussion

Ok that makes sense! Perhaps could revisit this if it becomes an issue later.

[ghost]

I've removed the home_dir function and made all references to .wash use the cfg_dir one. This PR should be ready now @brooksmtownsend

[brooksmtownsend]

LGTM, thank you again @mattwilkinsonn !