dev/report: adding initial flow of report

docs/dev/report.md

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+# opct report | development
+
+This document describe development details about the report.
+
+First of all, the report is the core component in the review process.
+It will extract all the data needed to the review process, transform
+it into business logic, aggregating common data, loading it to the
+final report data which is consumed to build CLI and HTML report output.
+
+The input data is the report tarball file, which should have all required data, including must-gather.
+
+The possible output channels are:
+
+- CLI stdout
+- HTML report file: stored at `<output_dir>/opct-report.html` (a.k.a frontend)
+- JSON dataset: stored at `<output_dir>/opct-report.json`
+- Log files: stored at `<output_dir>/failures-${plugin}`
+- Minimal HTTP file serveer serving the `<output_dir>` as root directory in TCP port 9090 
+
+Overview of the flow:
+
+``` mermaid
+%%{init: {"flowchart": {"useMaxWidth": false}}}%%
+
+sequenceDiagram
+  autonumber
+  Reviewer->>Reviewer/Output: 
+  Reviewer->>OPCT/Report: ./opct report [opts] --save-to <output_dir> <archive.tar.gz>
+  OPCT/Report->>OPCT/Archive: Extract artifact
+  OPCT/Archive->>OPCT/Archive: Extract files/metadata/plugins
+  OPCT/Archive->>OPCT/MustGather: Extract Must Gather from Artifact
+  OPCT/MustGather->>OPCT/MustGather: Run preprocessors (counters, aggregators)
+  OPCT/MustGather->>OPCT/Report: Data Loaded
+  OPCT/Report->>OPCT/Report: Data Transformer/ Processor/ Aggregator/ Checks
+  OPCT/Report->>Reviewer/Output: Extract test output files
+  OPCT/Report->>Reviewer/Output: Show CLI output
+  OPCT/Report->>Reviewer/Output: Save <output_dir>/opct-report.html/json
+  OPCT/Report->>Reviewer/Output: HTTP server started at :9090
+  Reviewer->>Reviewer/Output: Open http://localhost:9090/opct-report.html
+  Reviewer/Output->>Reviewer/Output: Browser loads data set report.json
+  Reviewer->>Reviewer/Output: Navigate/Explore the results
+```
+
+## Frontend
+
+> TODO: detail about the frontend construct.