feat: switch to firebase-admin module imports

[prescottprue]

Description

Could be a breaking change

Screenshots (if appropriate)

[DiegoGonzalezCruz]

Hi! Any news about this PR?

[prescottprue]

@DiegoGonzalezCruz Just now getting a chance to circle back on this - most of the changes have been made, just making a few more updates to tests/docs before releasing on beta tag

[codecov[bot]]

Codecov Report

Merging #564 (8547fb2) into alpha (ceddde2) will increase coverage by 44.18%. The diff coverage is 70.93%.

@@             Coverage Diff             @@
##            alpha     #564       +/-   ##
===========================================
+ Coverage   29.46%   73.64%   +44.18%     
===========================================
  Files          13        7        -6     
  Lines         560      296      -264     
  Branches      157      104       -53     
===========================================
+ Hits          165      218       +53     
+ Misses        385       58      -327     
- Partials       10       20       +10     

Impacted Files	Coverage Δ
src/firebase-utils.ts	47.77% <47.77%> (+39.13%)	:arrow_up:
src/tasks.ts	77.77% <77.77%> (+68.47%)	:arrow_up:
src/attachCustomCommands.ts	85.52% <85.07%> (+76.70%)	:arrow_up:
src/extendWithFirebaseConfig.ts	100.00% <100.00%> (+85.36%)	:arrow_up:
src/index.ts	100.00% <100.00%> (ø)
src/node-utils.ts	94.59% <100.00%> (+78.33%)	:arrow_up:
src/plugin.ts	100.00% <100.00%> (ø)
src/pluginWithTasks.ts
... and 2 more

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