Allow secrets to be set before deploying functions

[inlined]

Addressing old feedback I got in person at the Firebase Summit since it seems it never got picked up. Customers sometimes want to set a secret when they set up a new project, but the command fails until they try to deploy broken functions first.

The alternative solution, of course, is to declare a secret param, but this seems like a friendly guardrail given that the command exists.

[codecov-commenter]

Codecov Report

Patch coverage: 60.00% and no project coverage change.

Comparison is base (ac467a1) 54.98% compared to head (612dc68) 54.98%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5918   +/-   ##
=======================================
  Coverage   54.98%   54.98%           
=======================================
  Files         333      333           
  Lines       22985    22990    +5     
  Branches     4710     4710           
=======================================
+ Hits        12639    12642    +3     
- Misses       9217     9219    +2     
  Partials     1129     1129           

Impacted Files	Coverage Δ
src/functions/secrets.ts	82.17% <60.00%> (-0.90%)	⬇️

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