cr_build_yaml_secrets: Create an availableSecrets entry for build yaml

environment arguments in the builds.
Usage
cr_build_yaml_secrets(

R/yaml.R:

so they can use Secret Manager environment arguments in the builds.
#'
#' @param secretEnv The name of the secretEnv

tests/testthat/_snaps/build.md:

: ubuntu
args:
- bash

cr_buildstep: Create a yaml build step

-builders/",
entrypoint = NULL,
dir = "",

R/buildsteps.R:

for previous buildsteps to complete before running.  Default it will wait for previous step.
#' @param secretEnv A list

tests/testthat/test-build.R:

$SECRET $SECRET2",
secretEnv = c("SECRET", "SECRET2")
availableSecrets = list(s1, s2),