Add support for network/NatGateways

[super-harsh]

Closes #2893

What this PR does / why we need it:

This PR adds support for network/NatGateways and network/PublicIpPrefix

Note: Did try adding network/CustomIpPrefix as well, however, looks like their API has some issues, and its getting stuck in Provisioning state too much in the background making it unable to delete. Resource in portal. link to docs stating about it getting stuck.

If applicable:

• this PR contains tests

[codecov-commenter]

Codecov Report

Merging #2906 (c0b9d84) into main (b762503) will increase coverage by 0.00%.
The diff coverage is 53.43%.

@@            Coverage Diff            @@
##             main    #2906     +/-   ##
=========================================
  Coverage   54.34%   54.35%             
=========================================
  Files        1262     1270      +8     
  Lines      550814   552852   +2038     
=========================================
+ Hits       299360   300499   +1139     
- Misses     202453   203189    +736     
- Partials    49001    49164    +163     

Impacted Files	Coverage Δ
...etwork/v1api20220701/private_endpoint_types_gen.go	52.13% <ø> (ø)
...rk/v1api20220701/private_link_service_types_gen.go	59.39% <ø> (ø)
...rk/v1api20220701/nat_gateway_spec_arm_types_gen.go	33.33% <33.33%> (ø)
...api20220701/public_ip_prefix_spec_arm_types_gen.go	33.33% <33.33%> (ø)
...1api20201101storage/public_ip_address_types_gen.go	52.63% <50.00%> (-2.55%)	⬇️
...etwork/v1api20220701/public_ip_prefix_types_gen.go	50.40% <50.40%> (ø)
...work/v1api20220701storage/nat_gateway_types_gen.go	55.17% <55.17%> (ø)
...v1api20220701storage/public_ip_prefix_types_gen.go	55.17% <55.17%> (ø)
...api/network/v1api20220701/nat_gateway_types_gen.go	57.10% <57.10%> (ø)
.../customizations/nat_gateway_extension_types_gen.go	100.00% <100.00%> (ø)
... and 2 more

... and 15 files with indirect coverage changes

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[theunrepentantgeek]

Looks good - just one concern about a deleted file.