Add support for 2023-06-01-preview Postgres API

[matthchr]

This API enables support for Postgres 15 and 16.
This fixes #3627.

If applicable:

• this PR contains documentation
• this PR contains tests
• this PR contains YAML Samples

[matthchr]

/ok-to-test sha=cd36cc4

[codecov-commenter]

Codecov Report

Attention: 868 lines in your changes are missing coverage. Please review.

Comparison is base (517d028) 53.50% compared to head (1d68921) 53.50%.

Files	Patch %	Lines
...review/flexible_servers_configuration_types_gen.go	61.44%	122 Missing and 33 partials ⚠️
...0601preview/flexible_servers_database_types_gen.go	53.75%	122 Missing and 32 partials ⚠️
...review/flexible_servers_firewall_rule_types_gen.go	54.65%	120 Missing and 31 partials ⚠️
...iew/storage/flexible_servers_database_types_gen.go	43.29%	107 Missing and 24 partials ⚠️
...torage/flexible_servers_firewall_rule_types_gen.go	43.29%	107 Missing and 24 partials ⚠️
...torage/flexible_servers_configuration_types_gen.go	52.20%	106 Missing and 24 partials ⚠️
...30601preview/flexible_server_spec_arm_types_gen.go	33.33%	4 Missing ⚠️
...exible_servers_configuration_spec_arm_types_gen.go	33.33%	4 Missing ⚠️
...ew/flexible_servers_database_spec_arm_types_gen.go	33.33%	4 Missing ⚠️
...exible_servers_firewall_rule_spec_arm_types_gen.go	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             main    #3686     +/-   ##
=========================================
  Coverage   53.50%   53.50%             
=========================================
  Files        1364     1376     +12     
  Lines      461340   468032   +6692     
=========================================
+ Hits       246834   250418   +3584     
- Misses     177520   180012   +2492     
- Partials    36986    37602    +616     

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[matthchr]

/ok-to-test sha=1d68921

[matthchr]

/ok-to-test sha=1d68921