Add just recipe to update catalog .env

[stacimc]

Problem

We have the just env recipe to create .env files from templates, but in the Catalog we often don't want to fully override our existing .env because we would lose API keys that are set as env variables. It would be nice to have a way to update your catalog/.env to pull in any updates without overriding everything.

Description

A just catalog/env recipe, or else an update to the existing just env, that copies in everything from the env.template but does not overwrite API keys.

Alternatives

Alternatively we could have an entire section of the .env which is preserved, and move the API keys to this section. Something like:

#######################
# Permanent settings
# These settings will not be overwritten by `just catalog/env`
#######################

API_KEY_FOO = 'foo'
API_KEY_BAR = 'bar'

# Devs can place any other settings they don't want to lose to an env update here
MY_OTHER_SETTING_I_DONT_WANT_TO_LOSE = True

We can add this to the env.template. When just env or just catalog/env is run, if no catalog/.env already exists, we copy the whole thing. If there's an existing catalog/.env, we copy over everything else but don't touch this section. It should be at the end of the file, allowing permanent settings to override values in other sections.

Additional context