add model input & list models flags

[tarunKoyalwar]

Proposed Changes

• add flags to list models and pass a model name as input

MODEL:
   -g3, -gpt3         use GPT-3.5 model (default true)
   -g4, -gpt4         use GPT-4.0 model
   -m, -model string  specify model to use (ex: gpt-4-0314)
   -lm, -list-models  list available models

$  ./aix -lm

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[INF] Current aix version v0.0.3 (latest)
gpt-4-0613
curie-search-query
gpt-4
babbage-search-query
gpt-4-1106-preview
babbage-search-document
dall-e-2
gpt-3.5-turbo-0301
gpt-3.5-turbo-16k-0613
text-embedding-ada-002
davinci-search-query
gpt-3.5-turbo-instruct
gpt-3.5-turbo-16k
whisper-1
ada-search-document
gpt-3.5-turbo-0613
ada-code-search-code
davinci-002
gpt-3.5-turbo-instruct-0914
babbage-002
gpt-4-vision-preview
davinci-search-document
curie-search-document
gpt-3.5-turbo
ada-search-query
ada-code-search-text
tts-1-hd
dall-e-3
gpt-3.5-turbo-1106
tts-1-hd-1106
tts-1-1106
tts-1
gpt-4-0314