Modify snapshot config to allow using schema/database/alias macros

[gshank]

resolves #10301

Problem

Snapshots are special snowflakes and use "target_schema" and "target_database" instead of standard schema/database/alias.

Solution

Do not require setting "target_schema" and instead use standard schema setting (unless target_schema or target_database is set, then override).

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.79%. Comparing base (1aeff2c) to head (6aeba99).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10439      +/-   ##
==========================================
- Coverage   88.79%   88.79%   -0.01%     
==========================================
  Files         180      180              
  Lines       22562    22549      -13     
==========================================
- Hits        20034    20022      -12     
+ Misses       2528     2527       -1     

Flag	Coverage Δ
integration	86.06% <100.00%> (-0.01%)	⬇️
unit	62.17% <100.00%> (+0.07%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
Unit Tests	62.17% <100.00%> (+0.07%)	⬆️
Integration Tests	86.06% <100.00%> (-0.01%)	⬇️

[graciegoheen]

Confirmed everything is working as expected:

1. I can create a snapshot without target_schema
   
   

2. I can also create a snapshot with schema
   
   

3. target_schema still works for backwards compatibility