Updates the JWT/OIDC auth plugin

[austingebauer]

This PR updates the JWT/OIDC auth plugin to bring in its latest changes. It includes a new feature, two bug fixes, and additional changes needed to transition the plugin to using hashicorp/cap.

The associated PRs for the plugin are:

• Adds max_age role parameter and auth_time claim validation vault-plugin-auth-jwt#159
• Use the cap/oidc library for OIDC based authentication vault-plugin-auth-jwt#158
• Use the cap/jwt library for JWT based authentication vault-plugin-auth-jwt#155

The following steps were taken:

1. go get github.com/hashicorp/vault-plugin-auth-jwt@master
2. go mod tidy
3. go mod vendor