feat: Initialize Strata.Excel.Core library with export, import, and test utilities

This commit introduces the `Strata.Excel.Core` project, a .NET library built on ClosedXML for robust Excel document generation and data import.

Key features include:
- **Export:** Flexible data export to Excel, supporting custom formatting, titles, subtitles, humanized headings, and batched processing for large datasets. Includes `ExcelContentResult` and `ZipFileContentResult` for ASP.NET Core integration.
- **Import:** Utilities to easily import data from Excel worksheets into C# objects.
- **Test Utilities:** Comprehensive helpers for comparing Excel workbooks in tests, handling resource extraction, and performing load tests.
- **Build Infrastructure:** Sets up a Dockerfile for building the library, including SonarQube and Dependency-Check scanning.
- **Project Structure:** Establishes `.gitignore`, `.dockerignore`, `nuget.config`, and a `README.md` with usage instructions and versioning guidelines.

This foundational commit provides a reusable and well-tested framework for Excel operations within Strata applications.

README.md

@@ -1,2 +1,81 @@
-# excel.core
+# Strata.Excel.Core
+This provides a library for Strata standard ClosedXML Excel documents
 
+
+[![build](https://github.com/stratadecision/excel.core/actions/workflows/build.yaml/badge.svg)](https://github.com/stratadecision/excel.core/actions/workflows/build.yaml)
+
+
+[![SonarQube](https://img.shields.io/badge/SonarQube-Strata.excel.core-004880?logo=sonarqube)](https://sonarqube.sdt.local/dashboard?id=Strata.excel.core)
+
+[![Strata.Excel.Core](https://img.shields.io/badge/nuget-Strata.Excel.Core-004880?logo=nuget&logoColor=004880)](https://proget.ops.stratanetwork.net/feeds/nuget/Strata.Excel.Core/versions?HidePrerelease=True)
+[![Strata.Excel.TestUtilities](https://img.shields.io/badge/nuget-Strata.Excel.TestUtilities-004880?logo=nuget&logoColor=004880)](https://proget.ops.stratanetwork.net/feeds/nuget/Strata.Excel.TestUtilities/versions?HidePrerelease=True)
+
+
+
+## Branching and Versioning
+
+| branch     | version format        | example         |
+| ---------- | --------------------- | --------------- |
+| main     | #.#.#                 | 1.2.3           |
+| feature/\* | #.#+1.0-featureName.# | 1.3.0-newfeat.1 |
+| fix/\*     | #.#.#+1-fixName.#     | 1.2.4-bug.1     |
+
+See our [confluence page](https://confluence.sdt.local/display/DOP/Branching+and+Versioning) for more information
+
+## Usage
+
+### Build and Run
+
+```
+docker-compose up -d --build
+```
+
+- https://localhost:8443/index (swagger api)
+- https://localhost:8443/hangfire (hangfire dashboard)
+- http://localhost:8081 (redis commander)
+
+### Extracting nuget package
+
+```
+docker create --name throwaway strataexcel-excel-core
+docker cp throwaway:/pack .
+docker rm throwaway
+```
+
+### Cleanup
+
+```
+docker-compose down
+```
+
+
+# Helpful Features
+### Adding a drop down list to a worksheet
+
+ClosedXML offers the functionality for adding drop down lists to columns with validation out of the box. However, that implementation has a data length limitation of a formula field. For lists longer than trivial selections this extension method can be used:
+
+```csharp 
+/// <param name="items">Drop down list items</param>
+/// <param name="hiddenWorksheetName">Name of hidden worksheet that holds data</param>
+/// <param name="orderItems">Sort items in ascending order</param>
+CreateDataValidation(this IXLColumn column, IEnumerable<string> items, string hiddenWorksheetName, bool orderItems = true)
+```
+### Example usage
+```csharp
+var workbook = new XLWorkbook();
+var worksheet= wb.Worksheets.Add("Strata Data Worksheet");
+
+// Illustrating a list longer than standard Data Validation can handle
+var dropDownListItems = new List<string>(){"Department A", "Department B", "Department C", "Department D", "Department E", "Department F"
+"Department G", "Department H", "Department I", "Department J", "Department K", "Department L"
+"Department M", "Department N", "Department O", "Department P", "Department Q", "Department R"};
+
+// Add drop down with list items to all cells in column 1
+worksheet.Column(1).CreateDataValidation(dropDownListItems, "Name of Worksheet");
+```
+
+### Notes
+* Worksheets must have unique names in excel therefore an overload for worksheet name is provided. When adding more than one drop down to a single worksheet it will be necessary to ensure each worksheet has a unique name.
+* Data validation is implemented by adding a hidden worksheet to your workbook that contains all of the desired list items, validation is performed against the hidden worksheet's list.
+
+