Add environment configuration files to .gitignore (#2830)

* Add environment configuration files to .gitignore

* Delete config files from repo

* Refactor release cb file to delete config file lines from gitignore

* Reorder env files

* Add README for config files

core/src/main/java/google/registry/config/files/README.md

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+# Nomulus Environment Configuration
+
+The configuration files for the different Nomulus environments are not included in this repository. To configure and run a specific environment, you will need to create the corresponding YAML configuration file in this directory.
+
+The following is a list of the environment configuration files that you may need to create:
+
+*   `nomulus-config-alpha.yaml`
+*   `nomulus-config-crash.yaml`
+*   `nomulus-config-qa.yaml`
+*   `nomulus-config-sandbox.yaml`
+*   `nomulus-config-production.yaml`
+
+Please create the relevant file for the environment you intend to use and populate it with the necessary configuration details.

core/src/main/java/google/registry/config/files/nomulus-config-alpha.yaml

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-# Add environment-specific configuration here.

core/src/main/java/google/registry/config/files/nomulus-config-crash.yaml

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-# Add environment-specific configuration here.

core/src/main/java/google/registry/config/files/nomulus-config-production.yaml

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-# Add environment-specific configuration here.

core/src/main/java/google/registry/config/files/nomulus-config-qa.yaml

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-# Add environment-specific configuration here.

core/src/main/java/google/registry/config/files/nomulus-config-sandbox.yaml

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-# Add environment-specific configuration here.