feat: add highlight_type to files.completeUploadExternal and filesUploadV2

[zimeg]

This pull request adds highlight_type support to files.completeUploadExternal and the filesUploadV2 method.

The highlight_type parameter allows specifying the file type hint for uploads (e.g. png, jpg, gif), enabling optimistic rendering before the async upload processing job completes.

📚 https://docs.slack.dev/reference/methods/files.completeUploadExternal

Changes

• Added highlightType to FilesCompleteUploadExternalRequest.FileDetails (per-file in the files array)
• Added highlightType to FilesUploadV2Request (top-level for single-file uploads) and FilesUploadV2Request.UploadFile (for multi-file uploads)
• Updated MethodsClientImpl.filesUploadV2 to pass highlightType through to each FileDetails object in the completion step

Usage

import com.slack.api.Slack;
import com.slack.api.methods.response.files.FilesUploadV2Response;

Slack slack = Slack.getInstance();

// Single file upload with highlight_type
FilesUploadV2Response response = slack.methods(token).filesUploadV2(r -> r
    .channel("C0123456789")
    .file(new File("./image.png"))
    .filename("image.png")
    .title("Image Upload")
    .highlightType("png")
    .initialComment("Uploaded with highlight_type for optimistic rendering")
);

// Multiple file uploads with highlight_type
FilesUploadV2Response response = slack.methods(token).filesUploadV2(r -> r
    .channel("C0123456789")
    .uploadFiles(Arrays.asList(
        FilesUploadV2Request.UploadFile.builder()
            .file(new File("./photo.jpg"))
            .filename("photo.jpg")
            .title("Photo")
            .highlightType("jpg")
            .build(),
        FilesUploadV2Request.UploadFile.builder()
            .file(new File("./diagram.png"))
            .filename("diagram.png")
            .title("Diagram")
            .highlightType("png")
            .build()
    ))
    .initialComment("Multiple files with highlight_type")
);

Related PRs

• Node SDK: feat(web-api): add highlight_type to files.completeUploadExternal and filesUploadV2 node-slack-sdk#2594
• Python SDK: feat: add highlight_type to files.completeUploadExternal and files_upload_v2 python-slack-sdk#1875

Category (place an x in each of the [ ])

• bolt (Bolt for Java)
• bolt-{sub modules} (Bolt for Java - optional modules)
• slack-api-client (Slack API Clients)
• slack-api-model (Slack API Data Models)
• slack-api-*-kotlin-extension (Kotlin Extensions for Slack API Clients)
• slack-app-backend (The primitive layer of Bolt for Java)

Requirements

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you agree to those rules.

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 73.19%. Comparing base (c636708) to head (685d67f).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
.../com/slack/api/methods/impl/MethodsClientImpl.java	33.33%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1589      +/-   ##
============================================
+ Coverage     73.17%   73.19%   +0.01%     
- Complexity     4513     4514       +1     
============================================
  Files           477      477              
  Lines         14291    14294       +3     
  Branches       1488     1488              
============================================
+ Hits          10458    10462       +4     
- Misses         2940     2941       +1     
+ Partials        893      891       -2     

Flag	Coverage Δ
jdk-14	73.19% <33.33%> (+0.01%)	⬆️

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