[2.3.0] Make DB creation optional

[stancl]

Resolves #296

DB creation can be disabled for all tenants (tenancy.create_database config), or for individual tenants during tenant creation:

Tenant::new()->withData([
    '_tenancy_create_database' => false,
])->save();

[codecov]

Codecov Report

Merging #299 into 2.x will increase coverage by 0.05%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##                2.x     #299      +/-   ##
============================================
+ Coverage     87.45%   87.51%   +0.05%     
- Complexity      381      384       +3     
============================================
  Files            58       58              
  Lines          1108     1113       +5     
============================================
+ Hits            969      974       +5     
  Misses          139      139

Impacted Files	Coverage Δ	Complexity Δ
src/TenantManager.php	95.77% <100%> (+0.15%)	52 <2> (+3)	⬆️

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