chore: Add Dockerfile and publish workflow

[poppoerika]

momento-proxy Docker image is tested on an EC2 instance and I was able to set a key/value pair.

[root@ip-172-31-53-115 bin]# telnet 0.0.0.0 11211
Trying 0.0.0.0...
Connected to 0.0.0.0.
Escape character is '^]'.
set erika 0 0 3
eri 
STORED

Every time a pr is merged to main, a new Docker image is built and pushed to the gomomento/momento-proxy repo.
When users run docker run, they need to provide an env variable MOMENTO_AUTHENTICATION (Momento auth token).
Also updated momento-proxy.md to include how to run the momento-proxy Docker image.

[eaddingtonwhite]

@poppoerika This is looking good to me nice work! Lets get it merged and can do final verification again in our main momento branch make sure image gets published properly. Then can work to get contribute branch down into Bryan's fork.

Maybe have @danielamiao take one more pass on content quick just to get one more pair eyes.

[poppoerika]

@eaddingtonwhite @danielamiao
Updated the Dockerfile a bit so that we can mount a host machine's config directory to a container's config directory to be able to use a custom config file passed by users.
Also updated README to reflect this change.
Tested it on an EC2 instance and was able to use my custom config file to run.

[eaddingtonwhite]

Nice work @poppoerika