docs: api spec documentation

[mineme0110]

Description:

Update documentation for the credential offer and present proof endpoint to make it more clear when the goal and goal code applicable
#1486

Alternatives Considered (optional):

Link to existing ADR (Architecture Decision Record), if any. If relevant, describe other approaches explored and the selected approach. Documenting why the methods were not selected will create a knowledge base for future reference, helping prevent others from revisiting less optimal ideas.

Checklist:

• My PR follows the contribution guidelines of this project
• My PR is free of third-party dependencies that don't comply with the Allowlist
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked the PR title to follow the conventional commit specification

[github-actions]

Integration Test Results

20 files  ±0  20 suites  ±0   2s ⏱️ -1s
55 tests ±0  55 ✅ ±0  0 💤 ±0  0 ❌ ±0 
97 runs  ±0  97 ✅ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 7c9c6ad. ± Comparison against base commit 38b251b.

[github-actions]

Unit Test Results

104 files  ±0  104 suites  ±0   20m 48s ⏱️ + 1m 7s
882 tests ±0  874 ✅ ±0  8 💤 ±0  0 ❌ ±0 
889 runs  ±0  881 ✅ ±0  8 💤 ±0  0 ❌ ±0 

Results for commit 7c9c6ad. ± Comparison against base commit 38b251b.

[coveralls]

coverage: 48.642% (-0.1%) from 48.763%
when pulling 7c9c6ad on fix-open-api-spec-documentation
into 38b251b on main.