Adding prompt when transcribe with Whisper

[minhquoc0712]

• Add initial_prompt to WhisperLearner.infer. initial_prompt is a string that suggests the context of the transcription. For example names of people that will appear in the transcription.
• The ROS and ROS2 node, documents, and demo are updated accordingly.

[tsampazk]

The tests on speech_transcription/vosk fail. It seems that the certificates of the url used to download vosk models have expired. I think it's this one which indeed gives out a warning of expired certificates when visiting from the browser. It seems they expired today:

Websites prove their identity via certificates, which are valid for a set time period. 
The certificate for alphacephei.com expired on 9/26/2023.

Error code: SEC_ERROR_EXPIRED_CERTIFICATE

Found a similar issue here from last year.

One quick fix would be to disable verification here by adding the verify=False argument. However, it still fails down the line on this one. Following a quick search, i couldn't find an easy way to disable verification on that one. @minhquoc0712 could you please take a look at potential fixes and maybe include them on this PR?

[minhquoc0712]

@tsampazk , I run the test_voks.py, and it doesn't have any errors. I run it from my room's WiFi. Can you try again? Perhaps, Vosk developers made some fixes?

[tsampazk]

@minhquoc0712 thanks for testing, it seems that indeed they seem to have fixed the expired certificates. I will provide a review soon.