Dockerize sync tool.

This achieves a few things:

1. Creates Dockerfile for sync tool, so that it can be invoked from
   Tekton tasks.
2. Makes sync config directory configurable by flag, so that the tool
   can be ran from any directory. This defaults to sync/config (same as
   before).

Symlinks are retainined in the root directory for requirements.txt and
runtime.txt to satisfy Netlify Build requirements:
https://docs.netlify.com/configure-builds/manage-dependencies/#python

Issue: #34

requirements.txt

-wget==3.2
-PyYAML==5.1.2
-google-cloud-storage==1.23.0
-Jinja2==2.11.1
-google-auth==1.11.0

requirements.txt

+sync/requirements.txt
\ No newline at end of file

runtime.txt

-3.7
\ No newline at end of file

runtime.txt

+sync/runtime.txt
\ No newline at end of file

sync/Dockerfile

+FROM python:3.7
+
+WORKDIR /app
+# Only copy specific values instead of the entire directory.
+# We're primarily trying to avoid pulling in config/, since it's confusing that
+# it will not be used.
+COPY sync.py sync.py
+COPY requirements.txt requirements.txt
+
+RUN pip install -r requirements.txt
+
+ENTRYPOINT [ "python3", "sync.py" ]

sync/README.md

+# sync
+
 This directory includes a helper script for synchronizing contents
 from specified Tekton repositories to this repository.
 
@@ -5,7 +7,19 @@ To run this script locally, set up a Python 3 environment with appropriate
 Google Cloud Platform credentials, and execute the following command:
 
 ```bash
-cd ..
-pip install -r requirements.txt
-python sync/sync.py
+pip3 install -r requirements.txt
+python3 sync.py
+```
+
+## Usage
+
+```bash
+       USAGE: sync.py [flags]
+flags:
+
+sync.py:
+  -c,--config: Config directory
+    (default: 'config')
+
+Try --helpfull to get a list of all flags.
 ```

sync/requirements.txt

+wget==3.2
+PyYAML==5.1.2
+google-cloud-storage==1.23.0
+Jinja2==2.11.1
+google-auth==1.14.0
+absl-py==0.9.0
\ No newline at end of file

sync/runtime.txt

+3.7
\ No newline at end of file

sync/sync.py

@@ -8,14 +8,23 @@ import os
 import re
 import shutil
 
-from jinja2 import Environment, FileSystemLoader
+from absl import app
+from absl import flags
+from jinja2 import Environment
+from jinja2 import FileSystemLoader
 import wget
-from yaml import load, Loader
+from yaml import load
+from yaml import Loader
 
+FLAGS = flags.FLAGS
+
+# Flag names are globally defined!  So in general, we need to be
+# careful to pick names that are unlikely to be used by other libraries.
+# If there is a conflict, we'll get an error at import time.
+flags.DEFINE_string('config', os.path.dirname(os.path.abspath(__file__)) + '/config', 'Config directory', short_name='c')
 
 CONTENT_DIR = './content/en/docs'
 JS_ASSET_DIR = './assets/js'
-SYNC_DIR = './sync/config'
 TEMPLATE_DIR = './templates'
 VAULT_DIR = './content/en/vault'
 BUCKET_NAME = 'tekton-website-assets'
@@ -118,8 +127,8 @@ def scan(dir_path):
 
     return sync_config_paths
 
-if __name__ == '__main__':
-    sync_config_paths = scan(f'./{SYNC_DIR}')
+def main(argv):
+    sync_config_paths = scan(f'{FLAGS.config}')
     sync_configs = []
     for sync_config_path in sync_config_paths:
         with open(sync_config_path) as f:
@@ -130,3 +139,6 @@ if __name__ == '__main__':
     component_versions = get_component_versions(sync_configs)
     prepare_version_switcher_script(component_versions)
     prepare_vault_landing_page(component_versions)
+
+if __name__ == '__main__':
+  app.run(main)
\ No newline at end of file