feat(logging): custom log entries MONGOSH-1989

[alenakhineika]

Allow users to add custom entries to mongosh logs in their scripts.

log.info('This is an info message');
log.warn('Warning!');

The custom log message will sequentially appear alongside internal mongosh messages, and will look similar to this:

{"t":{"$date":"2025-01-06T16:14:23.023Z"},"s":"I","c":"MONGOSH","id":1000000012,"ctx":"shell-api","msg":"Loading file via load()","attr":{"nested":false,"filename":"/Users/alena.khineika/custom-logging.js"}}
{"t":{"$date":"2025-01-06T16:14:23.041Z"},"s":"I","c":"MONGOSH-SCRIPTS","id":1000000054,"ctx":"custom-log","msg":"This is an info message"}
{"t":{"$date":"2025-01-06T16:14:23.041Z"},"s":"W","c":"MONGOSH-SCRIPTS","id":1000000054,"ctx":"custom-log","msg":"Warning!"}