Add AI21 support to Inference Plugin

[Jan-Kazlouski-elastic]

Creation of new AI21 inference provider integration allowing completion (both streaming and non-streaming) and chat_completion (only streaming) to be executed as part of inference API.

Changes were tested locally against next models:
jamba-large
jamba-mini

• - Have you signed the contributor license agreement?
• - Have you followed the contributor guidelines?
• - If submitting code, have you built your formula locally prior to submission with gradle check?
• - If submitting code, is your pull request against main? Unless there is a good reason otherwise, we prefer pull requests against main and will backport as needed.
• - If submitting code, have you checked that your submission is for an OS and architecture that we support?
• - If you are submitting this code for a class then read our policy for that.