feat: dockerize p4bl0t

This commit removes DATABASE_URL variable in favour of a fixed name.
The project won’t panic anymore if this variable isn’t set. This
removes the need for dotenvy.

It also adds the necessary files to dockerize the application.

Update instructions in README on how to run the project.

Add possibility to compile the project without a database available.

Closes #8

.dockerignore

@@ -0,0 +1,32 @@
+# Include any files or directories that you don't want to be copied to your
+# container here (e.g., local build artifacts, temporary files, etc.).
+#
+# For more help, visit the .dockerignore file reference guide at
+# https://docs.docker.com/go/build-context-dockerignore/
+
+**/.DS_Store
+**/.classpath
+**/.dockerignore
+**/.env
+**/.git
+**/.gitignore
+**/.project
+**/.settings
+**/.toolstarget
+**/.vs
+**/.vscode
+**/*.*proj.user
+**/*.dbmdl
+**/*.jfm
+**/charts
+**/docker-compose*
+**/compose*
+**/Dockerfile*
+**/node_modules
+**/npm-debug.log
+**/secrets.dev.yaml
+**/values.dev.yaml
+/bin
+/target
+LICENSE
+README.md