feat: add /GET outgoing-payment-grant route

[BlairCurrey]

Changes proposed in this pull request

• adds new /GET outgoing-payment-grant route
• changes introspection to only require matching identifier if it's provided (from required if grant has identifier). This is important because the outgoing payment create grant is created with the wallet address url as the identifier (coming from the create request body), but we don't have the wallet address for this new route.

Context

fixes #3375

Checklist

• Related issues linked using fixes #number
• Tests added/updated
• Make sure that all checks pass
• Bruno collection updated (if necessary)
• Documentation issue created with user-docs label (if necessary)
• OpenAPI specs updated (if necessary)

[github-actions]

🚀 Performance Test Results

Test Configuration:

• VUs: 4
• Duration: 1m0s

Test Metrics:

• Requests/s: 37.87
• Iterations/s: 12.65
• Failed Requests: 0.00% (0 of 2281)

📜 Logs

> [email protected] run-tests:testenv /home/runner/work/rafiki/rafiki/test/performance
> ./scripts/run-tests.sh -e test "-k" "-q" "--vus" "4" "--duration" "1m"

Cloud Nine GraphQL API is up: http://localhost:3101/graphql
Cloud Nine Wallet Address is up: http://localhost:3100/
Happy Life Bank Address is up: http://localhost:4100/
cloud-nine-wallet-test-backend already set
cloud-nine-wallet-test-auth already set
happy-life-bank-test-backend already set
happy-life-bank-test-auth already set
     data_received..................: 796 kB 13 kB/s
     data_sent......................: 1.6 MB 27 kB/s
     http_req_blocked...............: avg=7.25µs   min=2.18µs  med=6.08µs   max=458.95µs p(90)=7.3µs    p(95)=7.76µs  
     http_req_connecting............: avg=414ns    min=0s      med=0s       max=273.14µs p(90)=0s       p(95)=0s      
     http_req_duration..............: avg=104.97ms min=12.71ms med=87.27ms  max=663.91ms p(90)=182.46ms p(95)=204.63ms
       { expected_response:true }...: avg=104.97ms min=12.71ms med=87.27ms  max=663.91ms p(90)=182.46ms p(95)=204.63ms
     http_req_failed................: 0.00%  ✓ 0         ✗ 2281
     http_req_receiving.............: avg=107.58µs min=31.34µs med=87.99µs  max=2.95ms   p(90)=129.64µs p(95)=169.85µs
     http_req_sending...............: avg=41.5µs   min=13.19µs med=30.82µs  max=2.43ms   p(90)=47.51µs  p(95)=65.64µs 
     http_req_tls_handshaking.......: avg=0s       min=0s      med=0s       max=0s       p(90)=0s       p(95)=0s      
     http_req_waiting...............: avg=104.82ms min=12.49ms med=87.15ms  max=663.79ms p(90)=182.23ms p(95)=204.5ms 
     http_reqs......................: 2281   37.867936/s
     iteration_duration.............: avg=316ms    min=203.4ms med=300.66ms max=1.13s    p(90)=369.2ms  p(95)=415.26ms
     iterations.....................: 762    12.650315/s
     vus............................: 4      min=4       max=4 
     vus_max........................: 4      min=4       max=4