feat: support for code-completion request delay and legacy mode

[zhengxs2018]

• Added a request delay config.
• Added Documentation for code completion.
• Code completion support for /v1/chat/completions and /v1/completions endpoint.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 73 lines in your changes are missing coverage. Please review.

Project coverage is 14.11%. Comparing base (883771d) to head (ede0702).

Files	Patch %	Lines
.../action/providers/AutoDevCodeSuggestionProvider.ts	0.00%	70 Missing :warning:
src/llm-provider/OpenAICompletion.ts	0.00%	3 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #40 +/- ## ========================================== - Coverage 14.14% 14.11% -0.03% ========================================== Files 335 335 Lines 32604 32666 +62 Branches 860 860 ========================================== Hits 4612 4612 - Misses 27992 28054 +62 ```

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