feat: support for annotations (#2007)

## Description

The MCP spec supports tool annotations like the below structure in the
2025-06-18 version of the spec.

https://modelcontextprotocol.io/specification/2025-06-18/schema#toolannotations

```
{
  destructiveHint?: boolean;
  idempotentHint?: boolean;
  openWorldHint?: boolean;
  readOnlyHint?: boolean;
}
```

Added a ToolAnnotations structure, an Annotations member to the
McpManifest structure, and a nil initializer for the Annotations member
to all calls to GetMcpManifest.

The ToolAnnotations structure and the member annotations are all defined
as pointers so that they are omited when not set. There are times when
the zero value is meaningful so this was the only way to make sure that
we distinguish between not setting the annotation and setting it with a
zero value.

## PR Checklist

> Thank you for opening a Pull Request! Before submitting your PR, there
are a
> few things you can do to make sure it goes smoothly:

- [x] Make sure you reviewed

[CONTRIBUTING.md](https://github.com/googleapis/genai-toolbox/blob/main/CONTRIBUTING.md)
- [x] Make sure to open an issue as a

[bug/issue](https://github.com/googleapis/genai-toolbox/issues/new/choose)
  before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea
- [x] Ensure the tests and linter pass
- [x] Code coverage does not decrease (if any source code was changed)
- [x] Appropriate docs were updated (if necessary)
- [x] Make sure to add `!` if this involve a breaking change

🛠️ Fixes #927

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

internal/tools/cloudsqlmssql/cloudsqlmssqlcreateinstance/cloudsqlmssqlcreateinstance.go

@@ -92,7 +92,7 @@ func (cfg Config) Initialize(srcs map[string]sources.Source) (tools.Tool, error)
 	if description == "" {
 		description = "Creates a SQL Server instance using `Production` and `Development` presets. For the `Development` template, it chooses a 2 vCPU, 8 GiB RAM (`db-custom-2-8192`) configuration with Non-HA/zonal availability. For the `Production` template, it chooses a 4 vCPU, 26 GiB RAM (`db-custom-4-26624`) configuration with HA/regional availability. The Enterprise edition is used in both cases. The default database version is `SQLSERVER_2022_STANDARD`. The agent should ask the user if they want to use a different version."
 	}
-	mcpManifest := tools.GetMcpManifest(cfg.Name, description, cfg.AuthRequired, allParameters)
+	mcpManifest := tools.GetMcpManifest(cfg.Name, description, cfg.AuthRequired, allParameters, nil)
 
 	return Tool{
 		Config:      cfg,