[Connect SDK] Integrate with backend calls for client secret

[simond-stripe]

Summary

Adds networking to the example backend (https://stripe-connect-mobile-example-v1.glitch.me/) for getting the publishable key, accounts, and client secret for the SDK.

Motivation

Demonstrates a canonical integration of the ConnectSDK.

Testing

• [ ] Added tests
• [ ] Modified tests
• [x] Manually verified

Screenshots

UI

https://github.com/user-attachments/assets/663166ea-333f-4b6a-a4d7-a665ad87887f

Network call logging

[github-actions[bot]]

Risky Change

This is considered a risky change because it adjusts the sample app build.gradle, please review carefully. We've seen issues in the past which resulted in failed builds for merchants. Please make sure the build.gradle change is intended.

By adding the label accept-risky-change to this PR, I acknowledge that I'm changing an example app and have verified that the SDK remains in a shippable state.

[github-actions[bot]]

Diffuse output:

OLD: identity-example-release-base.apk (signature: V1, V2)
NEW: identity-example-release-pr.apk (signature: V1, V2)

          │          compressed          │         uncompressed         
          ├───────────┬───────────┬──────┼───────────┬───────────┬──────
 APK      │ old       │ new       │ diff │ old       │ new       │ diff 
──────────┼───────────┼───────────┼──────┼───────────┼───────────┼──────
      dex │     2 MiB │     2 MiB │  0 B │   4.1 MiB │   4.1 MiB │  0 B 
     arsc │     1 MiB │     1 MiB │  0 B │     1 MiB │     1 MiB │  0 B 
 manifest │   2.3 KiB │   2.3 KiB │  0 B │     8 KiB │     8 KiB │  0 B 
      res │ 301.8 KiB │ 301.8 KiB │  0 B │ 455.5 KiB │ 455.5 KiB │  0 B 
   native │   6.2 MiB │   6.2 MiB │  0 B │  15.8 MiB │  15.8 MiB │  0 B 
    asset │     7 KiB │     7 KiB │  0 B │   6.8 KiB │   6.8 KiB │  0 B 
    other │  85.5 KiB │  85.5 KiB │ -2 B │ 158.7 KiB │ 158.7 KiB │  0 B 
──────────┼───────────┼───────────┼──────┼───────────┼───────────┼──────
    total │   9.6 MiB │   9.6 MiB │ -2 B │  21.5 MiB │  21.5 MiB │  0 B 

 DEX     │ old   │ new   │ diff      
─────────┼───────┼───────┼───────────
   files │     1 │     1 │ 0         
 strings │ 20108 │ 20108 │ 0 (+0 -0) 
   types │  6205 │  6205 │ 0 (+0 -0) 
 classes │  4991 │  4991 │ 0 (+0 -0) 
 methods │ 30124 │ 30124 │ 0 (+0 -0) 
  fields │ 17572 │ 17572 │ 0 (+0 -0) 

 ARSC    │ old  │ new  │ diff 
─────────┼──────┼──────┼──────
 configs │  164 │  164 │  0   
 entries │ 3624 │ 3624 │  0

APK

``` compressed │ uncompressed │ ──────────┬──────┼──────────┬──────┤ size │ diff │ size │ diff │ path ──────────┼──────┼──────────┼──────┼───────────────────── 28.3 KiB │ -3 B │ 62.6 KiB │ 0 B │ ∆ META-INF/CERT.SF 1.2 KiB │ +1 B │ 1.2 KiB │ 0 B │ ∆ META-INF/CERT.RSA ──────────┼──────┼──────────┼──────┼───────────────────── 29.5 KiB │ -2 B │ 63.8 KiB │ 0 B │ (total) ```

[simond-stripe]

@lng thanks for the thorough feedback! This isn't live yet and there's a number of PRs queued up behind this one, so I'll address this PR in a follow-up PR later today.