431 Add environment variable options to Spacewalk

[b-yap]

closes #431

adding the ff. arguments an ENV option:

1. KEYRING
2. KEYFILE
3. KEYNAME
4. SPACEWALK_PARACHAIN_URL
5. STELLAR_VAULT_SECRET_KEY_FILEPATH
6. STELLAR_OVERLAY_CONFIG_FILEPATH
7. AUTO_REGISTER

note for AUTO_REGISTER: since the value must be a tuple, make sure to enclose it with double quotes.

🙅 ❌ export AUTO_REGISTER=0,GA5ZSEJYB37JRC5AVCIA5MOP4RHTM335X2KGX3IHOJAPP5RE34K4KZVN:USDC,1000000 ❌ 🙅

✅ 👌 export AUTO_REGISTER="0,GAKNDFRRWA3RPWNLTI3G4EBSD3RGNZZOY5WKWYMQ6CQTG3KIEKPYWAYC:USDC,1000000" 👌 ✅

For arguments that accept option, make sure to enclose it with double quotes with the ACTUAL value.
🙅 ❌ export MAX_NOTIFS_PER_SUBSCRIPTION="1" ❌ 🙅
🙅 ❌ export MAX_NOTIFS_PER_SUBSCRIPTION="Some(1)" ❌ 🙅

✅ 👌 export MAX_NOTIFS_PER_SUBSCRIPTION=1 👌 ✅

[TorstenStueber]

Looks good.

[ebma]

Looks good, but is there a reason not to make all configuration parameters available as environment variables? We don't really use the ones that you didn't add but they could be useful for other users.

[b-yap]

@ebma I added env option for ALL args.

[ebma]

Since I guess there is no way to spit out all available names of environment variables from the vault binary, I think it's best to give each env variable the very same name as the config item. Then it's at least somewhat obvious which names are used/available.