add show_on to ToolParameter

[zyqzyq]

Summary

Adds optional conditional form visibility for tool parameters by extending ToolParameter with show_on: list[FormShowOnObject] (default empty), reusing the existing FormShowOnObject model from dify_plugin.entities.model.provider. Tool YAML that omits show_on continues to deserialize as an empty list.

Pull Request Checklist

Thank you for your contribution! Before submitting your PR, please make sure you have completed the following checks:

Compatibility Check

Fixes langgenius/dify#36141

• I have checked whether this change affects the backward compatibility of the plugin declared in README.md
  Note: This is an additive, optional field with default_factory=list. Existing tool manifests without show_on remain valid. No removal or semantic change of existing fields.

• I have checked whether this change affects the forward compatibility of the plugin declared in README.md
  Note: Older Dify runtimes that do not understand show_on in tool YAML may ignore unknown keys depending on their parser; the SDK simply models the field when present. If a specific minimum Dify version is required for UI behavior, that should be confirmed with maintainers and documented separately.

• If this change introduces a breaking change, I have discussed it with the project maintainer and specified the release version in the README.md
  N/A: No breaking change.

• I have described the compatibility impact and the corresponding version number in the PR description
  Impact: Backward-compatible schema extension; no SDK major bump implied by this change alone. Release version follows normal semver when the maintainers cut a release (current package version in tree: 0.8.0).

• I have checked whether the plugin version is updated in the README.md
  Note: No update to README.md version or manifest tables is included in this PR, because the change does not alter meta.version / meta.minimum_dify_version semantics by itself. Bump those only if product policy ties show_on to a new manifest or minimum Dify row.

Available Checks

• just build has passed

• Relevant documentation has been updated (if necessary)
  Note: Not updated; field name and type align with existing provider credential show_on patterns. Add docs if the project requires an explicit tool-parameter YAML example.

[gemini-code-assist]

Code Review

This pull request introduces a show_on field to the tool parameter configuration, enabling conditional display logic for parameters. The reviewer suggested adding a description attribute to this new field to maintain consistency with existing fields and ensure proper documentation generation.

[gemini-code-assist]

To maintain consistency with other fields in the ToolParameter class and to ensure proper documentation generation via the @docs decorator, please add a description to the show_on field.

Suggested change

	show_on: list[FormShowOnObject] = Field(default_factory=list)
	show_on: list[FormShowOnObject] = Field(default_factory=list, description="The conditions to show the parameter")