chore: rework plugin readmes, json changelogs and standalone repo setup

plugins/vault/CONTRIBUTING.md

@@ -0,0 +1,27 @@
+# Contributing to HashiCorp Vault
+
+## Development
+
+```bash
+npm run build      # build into dist/
+npm run test       # run this plugin's tests
+npm run typecheck  # type-check this plugin
+npm run validate   # check manifest.json
+npm run format     # format the code with Prettier
+```
+
+## Settings
+
+### Admin
+
+- **Redirect URI:** add `<base URL>/plugin-api/vault/oidc/callback` to `allowed_redirect_uris` in each Vault OIDC role
+- **Use the old redirect URI:** keep sending the 2.8 URI `<base URL>/vault/oidc/callback`. Upgraded installs keep this on until you turn it off
+
+### Host
+
+- **Vault signer profile:** the profile this host uses
+
+## Permissions
+
+- `vault.use`: create signer profiles and connect to hosts that use Vault. Admins and users have it by default.
+- `vault.share`: share a profile so every user can pick it. Only admins have it by default.