feat(copilot): add support for gemini 2.0 flash (#855) (#856)

Author: S1M0N38

doc/codecompanion.txt

@@ -2356,6 +2356,7 @@ We’ll explore some of the options in the Copilot adapter’s schema table:
         choices = {
           "gpt-4o-2024-08-06",
           "claude-3.5-sonnet",
+          "gemini-2.0-flash-001",
           ["o1-preview-2024-09-12"] = { opts = { stream = false } },
           ["o1-mini-2024-09-12"] = { opts = { stream = false } },
         },

doc/extending/adapters.md

@@ -415,6 +415,7 @@ schema = {
     choices = {
       "gpt-4o-2024-08-06",
       "claude-3.5-sonnet",
+      "gemini-2.0-flash-001",
       ["o1-preview-2024-09-12"] = { opts = { stream = false } },
       ["o1-mini-2024-09-12"] = { opts = { stream = false } },
     },

lua/codecompanion/adapters/copilot.lua

@@ -211,6 +211,7 @@ return {
         ["o1-mini-2024-09-12"] = { opts = { can_reason = true } },
         "claude-3.5-sonnet",
         "gpt-4o-2024-08-06",
+        "gemini-2.0-flash-001",
       },
     },
     reasoning_effort = {