Add decisions made for externalizing OpenSCD plugins (#1599)

* Added ADR-0003 - Externalize OpenSCD core plugins
* Added ADR-0004 - Technical solution for releasing and deployments

Author: david-monichi

docs/decisions/0003-extract-plugins.md

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+# ADR-0003 - Externalize OpenSCD core plugins
+
+Date: 2024-11-19
+
+## Status
+
+Approved
+
+## Context
+
+For a better expandability we would like to extract all plugins in a new plugins repository.
+
+## Decision
+
+Following the architectural decision in [OpenSCD Theming](./../0001-ADR-Theming.md) we will extract all OpenSCD Core plugins to an external repository.
+Doing so OpenSCD Core will be streamlined and a clean interface and structure for plugins will be provided for custom extensions.
+Before extracting this plugins a shared UI-Components module will be extracted. This UI-Components provide reusable UI-Components based on [NX](https://nx.dev/) for faster development for OpenSCD Core and custom plugins. This new repository will be created as mono repository to facility the plugins development and simplify the release and deployment process.
+
+Plugins will be moved to repository [OpenSCD official Plugins](https://github.com/openscd/oscd-official-plugins) and the release strategy is defined [here](./0004-openscd-release-and-deploy-strategy.md).
+As final task the current documentation will be added with a new section `How to add new and custom OpenSCD plugins` to support developers to follow the concept.
+
+## Consequences
+
+- Clean Code in OpenSCD Core
+- Clear architectural structure of plugins
+
+- Building OpenSCD is more then building a simple repository
+- Clear path must be defined how to extend OpenSCD with custom plugins (full software cycle till deployment)
+- Release process for OpenSCD Core and OpenSCD official plugins
+
+## Agreed procedure
+
+- move the plugins without any components abstraction to the external plugins repository
+  - copy all required dependencies regardless of code duplication
+- integrate the plugins as submodules within OpenSCD core in the pipeline
+- later on we can extract step by step for each plugin UI-Components

docs/decisions/0004-openscd-release-and-deployment-strategy.md

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+# ADR-0004 - Technical solution for releasing and deployments
+
+Date: 2024-11-19
+
+## Status
+
+Approved
+
+## Context
+
+Based on the [decision](./0003-extract-plugins.md) to externalize plugins in proper plugins repository a new release and deployment strategy needs to be defined.
+This plugins repository is solved as mono repository.
+
+## Decision
+
+### Release process 
+
+Since OpenSCD is based on [NX](https://nx.dev/) the release strategy needs to rely on NX as well and must allow single releases of sub modules within this mono repository.
+Such feature is provided by [NX release](https://nx.dev/recipes/nx-release) specially when using the [NX independently release feature](https://nx.dev/recipes/nx-release/release-projects-independently).
+
+A possible release command would look like:
+```
+  nx release --projects=plugin-1,plugin-3
+```
+
+## Consequences
+
+- Process needs to be documented so that all developers can easily follow it
+- The building of complete OpenSCD Editor, OpenSCD Core + OpenSCD plugins, depends now on two repositories
+- Custom OpenSCD eg. CoMPAS OpenSCD will be cleaner and more code can be reused
+- Similar Look & Feel of plugins if shared UI-Components are used
+- Faster plugin development and integration into OpenSCD Core