OIDC Token Exchange does not support multiple tokens

[mgriffin13]

Is your feature request related to a problem? Please describe.
PR #59 added the ability to use TFC Dynamic Workload Credentials, but the implementation was limited to the default configuration within Terraform. My use-case is that I'm attempting to use multiple Dynamic Workload Credentials within the same workspace, which TFC supports.

See https://developer.hashicorp.com/terraform/cloud-docs/workspaces/dynamic-provider-credentials/manual-generation#generating-multiple-tokens

Describe the solution you'd like
Given my use-case, I would like to see the JFrog provider accept a parameter where I can supply a TFC config such as "JFROG", then the JFrog provider would look for TFC_WORKLOAD_IDENTITY_TOKEN_JFROG, rather than just default to TFC_WORKLOAD_IDENTITY_TOKEN

Describe alternatives you've considered
Alternatives include just continuing to use static credentials

[alexhung]

@mgriffin13 Thanks for the suggestion. I've addd this to our plan.