Add missing JSON.stringify in database:settings:set

[jmwski]

Description

Fixes #3228

The namespace server expects string-value .settings/<setting>.json values to be quoted. For defaultWriteSizeLimit, this meant that passing unlimited broke with this error log in firebase-debug.log:

[debug] [2021-03-17T22:10:45.519Z] <<< [apiv2][body] PUT https://fir-multi-shards.firebaseio.com/.settings/defaultWriteSizeLimit.json {"error":"defaultWriteSizeLimit should be one of {\"small\", \"unlimited\", \"large\", \"medium\"}"}
[debug] [2021-03-17T22:10:45.636Z] FirebaseError: HTTP Error: 400, defaultWriteSizeLimit should be one of {"small", "unlimited", "large", "medium"}
    at module.exports (/usr/local/google/home/wyszynski/.nvm/versions/node/v10.15.3/lib/node_modules/firebase-tools/lib/responseToError.js:38:12)
    at Client.doRequest (/usr/local/google/home/wyszynski/.nvm/versions/node/v10.15.3/lib/node_modules/firebase-tools/lib/apiv2.js:238:23)
    at process._tickCallback (internal/process/next_tick.js:68:7)
[error]

Sample Commands

I tried setting the two supported database settings:

node ./lib/bin/firebase.js --project fir-multi-shards database:settings:set strictTriggerValidation false --instance fir-multi-shards

And:

node ./lib/bin/firebase.js --project fir-multi-shards database:settings:set defaultWriteSizeLimit unlimited --instance fir-multi-shards

And they both set the setting to the appropriate value. This change should also be robust to setting rules from the CLI.

[fredzqm]

Oh, maybe update the CHANGE_LOG.md

[bkendall]

One comment on the changelog, but looks fine otherwise