feat: add NDVI process endpoint and OpenAPI documentation

- Implemented the NDVI process execution endpoint in `path_info.rs`.
- Added OpenAPI specifications for the NDVI process inputs and outputs.
- Created a `justfile` for managing API client generation and backend tasks.
- Generated initial OpenAPI specification and saved it to `openapi.json`.

Author: ChristianBeilschmidt

.github/copilot-instructions.md

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+# Copilot Instructions
+
+This BioIS monorepo is written in Rust, SQL, TypeScript and Python.
+
+## Repository Structure
+
+| Path              | Description                                      |
+| ----------------- | -------------------------------------------------|
+| `README.md`       | Project Documentation                            |
+| `LICENSE`         | License File                                     |
+| `.github/`        | GitHub Configuration                             |
+| `justfile`        | Justfile for task automation                     |
+| `backend/`        | Rust API Code                                    |
+| `frontend/`       | TypeScript Angular Frontend Code                 |
+| `api-client/`     | OpenAPI client code generated from the API spec  |
+| `test-client/`    | Snippet-based test client for testing the API    |

.github/instructions/api-client.instructions.md

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+---
+applyTo: "api-client/**/*"
+---
+
+# Copilot Instructions
+
+- Never modify the `typescript` directory manually.
+  It is generated from the OpenAPI specification in `openapi.json` using the OpenAPI Generator.
+  To regenerate the API client, run `just generate-api-client` from the project root.
+- The OpenAPI Generator configuration is defined in `config.yaml`.
+  If you need to change the generated code, modify the configuration and regenerate the client.

.github/instructions/backend.instructions.md

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+---
+applyTo: "backend/**/*.rs, backend/**/*.sql"
+---
+
+# Copilot Instructions
+
+## Coding Style
+
+### Rust
+
+- Follow the Rust API guidelines for naming conventions, error handling, and documentation.
+- Use `snake_case` for variable and function names, and `PascalCase` for struct and enum names.
+- Ensure that all public functions and types have documentation comments using `///`.
+- Use `Result<T>` (from anyhow) for error handling and define custom error types where appropriate.
+- Use `camelCase` for JSON field names when serializing/deserializing with serde, and use `#[serde(rename_all = "camelCase")]` on structs to enforce this convention.
+- Never use `unwrap()` or `expect()` in production code. Instead, propagate errors using the `?` operator or handle them gracefully.
+- Start test function names with `it_` and use descriptive names that indicate what the test is verifying.
+
+### SQL
+
+- The SQL dialect used in this project is PostgreSQL. Follow the PostgreSQL SQL style guide for formatting and conventions.
+- For SQL queries, use uppercase for SQL keywords (e.g., SELECT, FROM, WHERE) and lowercase for table and column names.
+- SQLFluff is used for linting SQL files. Ensure that your SQL code adheres to the configured SQLFluff rules.

api-client/config.yaml

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+inputSpec: /local/openapi.json
+outputDir: /local/typescript
+generatorName: typescript
+gitHost: github.com
+gitUserId: geo-engine
+gitRepoId: BioIS
+additionalProperties:
+  supportsES6: true
+  npmName: "@geoengine/biois"
+  npmVersion: 0.1.0
+openapiNormalizer:
+  REF_AS_PARENT_IN_ALLOF: true