Add WIP documentation for packages' generation

scripts/README.md

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+# `wazuh-indexer` packages generation guide
+
+The packages' generation process consists on 2 steps:
+
+* **Build**: compiles the Java application and bundles it into a package.
+* **Assembly**: uses the package from the previous step and inflates it with plugins and 
+configuration files, ready for production deployment.
+
+We usually generate the packages using GitHub Actions, however, the process is designed to
+be independent enough for maximum portability. GitHub Actions provides infrastructure, while
+the building process is self-contained in the application code.
+
+Each section includes instructions to generate packages locally, using Act or Docker.
+
+- [Install Act](https://github.com/nektos/act)
+
+## Build
+
+...
+...
+
+#### Act (GitHub Workflow locally)
+
+```console
+act -j build -W .github/workflows/build.yml --artifact-server-path ./artifacts
+
+[Build slim packages/build] 🏁  Job succeeded
+```
+
+
+#### Running in Docker
+
+Within the [Docker environment](../docker):
+
+```console
+bash scripts/build.sh -v 2.11.0 -s false -p linux -a {x64|arm64} -d {rpm|deb|tar}
+```
+
+The generated package is sent to `artifacts/`
+
+
+## Assemble
+
+<!-- 
+### TAR
+### DEB
+-->
+
+### RPM
+
+The `assemble.sh` script will use the output from the `build.sh` script and use it as a 
+base to bundle together a final package containing the plugins, the production configuration 
+and the service files.
+
+The script will:
+
+- Extract the rpm package using `rpm2cpio` and `cpio` tools.
+
+    > By default, `rpm2cpio` and `cpio` tools expect the package to be in `wazuh-indexer/artifacts/tmp/rpm`. The script takes care of creating the required folder structure, copying also the min package and the SPEC file.
+
+    Current folder loadout at this stage:
+    ```
+    /rpm/$ARCH
+        /etc
+        /usr
+        /var
+        wazuh-indexer-min-*.rpm
+        wazuh-indexer.rpm.spec
+    ```
+
+    `usr`, `etc` and `var` folders contain `wazuh-indexer` files, extracted from `wazuh-indexer-min-*.rpm`.
+    `wazuh-indexer.rpm.spec` is copied over from `wazuh-indexer/distribution/packages/src/rpm/wazuh-indexer.rpm.spec`. 
+    The `wazuh-indexer-performance-analyzer.service` file is also copied from the same folder. It is a dependency of the SPEC file.
+
+- Install the plugins using the `opensearch-plugin` CLI tool.
+- Set up configuration files.
+
+    > Included in `min-package`. Default files are overwritten.
+    
+- Bundle an RPM file with `rpmbuild` and the SPEC file `wazuh-indexer.rpm.spec`.
+    - `rpmbuild` is part of the `rpm` OS package.
+
+    > `rpmbuild` is invoked from `wazuh-indexer/artifacts/tmp/rpm`. It creates the {BUILD,RPMS,SOURCES,SRPMS,SPECS,TMP} folders and applies the rules in the SPEC file. If successful, `rpmbuild` will generate the package in the `RPMS/` folder. The script will copy it to `wazuh-indexer/artifacts/dist` and clean: remove the `tmp\` folder and its contents.
+
+    Current folder loadout at this stage:
+    ```
+    /rpm/$ARCH
+        /{BUILD,RPMS,SOURCES,SRPMS,SPECS,TMP}
+        /etc
+        /usr
+        /var
+        wazuh-indexer-min-*.rpm
+        wazuh-indexer.rpm.spec
+    ```
+
+### Running in Act
+
+```console
+act -j assemble -W .github/workflows/build.yml --artifact-server-path ./artifacts
+
+[Build slim packages/build] 🏁  Job succeeded
+```
+
+#### Running in Docker
+
+Pre-requisites:
+
+* Current directory: `wazuh-indexer/`
+* Existing rpm package in `wazuh-indexer/artifacts/dist/rpm`, as a result of the _Build_ stage.
+
+```console
+MIN_PKG_PATH="./artifacts"
+docker run --rm \
+    -v ./scripts/:/home/wazuh-indexer/scripts \
+    -v $MIN_PKG_PATH:/home/wazuh-indexer/artifacts \
+    -v ./distribution/packages/src:/home/wazuh-indexer/distribution/packages/src \
+    -w /home/wazuh-indexer \
+    -it ubuntu:jammy /bin/bash
+
+apt-get update
+apt-get install -y rpm2cpio rpm cpio
+bash scripts/assemble.sh -v 2.11.0 -p linux -a x64 -d rpm
+```
+