509- Set up to use nvm for deploys and circleci

[Janell-Huyck]

Fixes #509

Our servers are now using nvm to set node versions. This PR is to set up Treatment Database to take advantage of this new configuration.

• Adds .nvmrc file to specify node version to use. I know that at least 18 will be needed in a future Treatment Database version, but the latest Node LTS version is actually 20.14.0, so I set our .nvmrc to that.
• Adds a capistrano rake task to install (if necessary) and use the version of node listed in the .nvmrc file.
• Modifies the circleci config file to download nvm and install & use the version of node that is listed in the .nvmrc file. This is to keep our deployment in step with our testing.
• Updates README

[hortongn]

@Janell-Huyck Has this PR been test deployed to libappstest or does it have the deploy bug you're working on?

[Janell-Huyck]

It's been deployed successfully and does not have the same issue as the deploy but I'm working on.

[Janell-Huyck]

Updated to allow Rails version to bump - went from ~>6.1.7.7 to ~>6.1.7. There was a Brakeman error for the older Rails version. After updating the Rails pinned version, I ran bundle update.