feat: Add support for Gemini-Exp-1114 model (#1187)

[MuggleJinx]

Description

This PR adds the newest Gemini-Exp-114 model, which is an experimental model from Google Gemini.

Motivation and Context

Closes issue #1187.

Types of changes

What types of changes does your code introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds core functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (update in the documentation)
• Example (update in the folder of example)

Implemented Tasks

• Add one new model type in Gemini model series.
• Edit the corresponding example, and test file.

Checklist

Go over all the following points, and put an x in all the boxes that apply.
If you are unsure about any of these, don't hesitate to ask. We are here to help!

• I have read the CONTRIBUTION guide. (required)
• My change requires a change to the documentation.
• I have updated the tests accordingly. (required for a bug fix or a new feature)
• I have updated the documentation accordingly.

[CaelumF]

Looks good, works for me.

Worth noting the experimental models page says that the models can be removed at any time, do you think this warrants some sort of warning or notice from our end too @Wendong-Fan ?