Add tsh workload-identity issue-jwt

[strideynet]

Closes #66311

Changelog: Introduces tsh workload-identity issue-jwt command for human issuance of JWT-SVIDs

Manual Test Plan

Test Environment

Local cluster with following Workload Identity spec:

kind: workload_identity
version: v1
metadata:
  name: human
  labels:
    env: human
spec:
  rules:
    allow:
      - conditions:
          - attribute: user.is_bot
            eq:
              value: "false"
  spiffe:
    id: /human/{{ user.name }}

Test Cases

• Issuance using name selector
• Issuance using label selector
• Issuance with multiple audiences
• Issuance of workload identity that does not exist/user does not have privileges for fails sensibly
• Directory is created if does not exist