fix tag operations in secretsmanager

[macnev2013]

Description

This PR resolves the problem outlined in localstack/localstack#10477.

Breaking Scenarios

Scenario 1

• Secret creation without tags.
• Addition of tags to the secret.
• Removal of all tags from the secret.
• Describing the secret reveals a Tags key with an empty list []. (Previously, this functionality was defective in moto.)

Scenario 2

• Secret creation without tags.
• Addition of tags to the secret.
• Complete tag removal using untag_resource by specifying all tags.
• On describing the secret, it should not contain of any tags. (Previously, this was not correctly implemented in moto.)

Fixes

• Changing the default value of tags to None to identify weather the tags ever added.
• Addition of NoneType handling in filtering functions
• Updated logic for untag_resource to remove multiple tags at once.

Testing

• Updated existing test cases to cover the scenario fixed

[codecov]

Codecov Report

Attention: Patch coverage is 93.75000% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 94.07%. Comparing base (9aef694) to head (61538c9).
Report is 143 commits behind head on master.

Files	Patch %	Lines
moto/secretsmanager/models.py	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7547      +/-   ##
==========================================
- Coverage   95.88%   94.07%   -1.82%     
==========================================
  Files         843     1070     +227     
  Lines       82578    91824    +9246     
==========================================
+ Hits        79178    86380    +7202     
- Misses       3400     5444    +2044     

Flag	Coverage Δ
servertests	29.57% <0.00%> (-2.96%)	⬇️
unittests	94.04% <93.75%> (-1.81%)	⬇️

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[bblommers]

LGTM - thank you @macnev2013!

[github-actions]

This is now part of moto >= 5.0.5.dev10