feat: add MCP prompts support

[nader-ziada]

Fixes: #226

Add MCP prompts support to enable pre-defined workflow templates and guidance for AI assistants.

Includes:

• Core prompt types (ServerPrompt, Prompt, PromptArgument, PromptMessage)
• Template argument substitution with {{variable}} syntax
• Required argument validation
• built-in prompts for common Kubernetes workflows (troubleshooting, deployment, scaling, cluster health, networking, resource usage)
• Integration with MCP server to register and serve prompts
• prompts in toml config file

[nader-ziada]

/hold

@Cali0707 I'm making an adjustment to the design to match the requirement from the issue here: #226

[nader-ziada]

@Cali0707 added reading prompts from toml file, please review when you get a chance

[manusa]

This PR is introducing 3 features at once (configurable prompts, toolset prompts, predefined prompts for our current toolsets).
I'd rather prefer if we could tackle those separately (1 PR each).

I also think we shouldn't add the core prompts yet, there's already PRs with some contributions that should be considered first #434)

I managed to spend some time properly defining the specs for each of the features that should be implemented:

• #226
• #556

I tried to account and polish most of what was already proposed in the scope of this PR.
However, I might have missed something. Let's discuss in the issue if something is missing.

I think it should be easy to break this PR down into the separate enhancements, which will make it easier to review, test, and release.
Please, if possible, break it down and add anything that might be missing from the isolated specs defined on each issue.