[Network/Storage] Rename private access vnet and add network rule storage commands

[tjprescott]

Closes #4067.

This PR renames the "private access" features introduced in a recent release to "service endpoints". This is a breaking change.

Additionally, this PR adds storage account commands to manage network rules, used in conjunction with the service endpoint feature.

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General Guidelines

• The PR has modified HISTORY.rst with an appropriate description of the change (see Modifying change log).

Command Guidelines

• Each command and parameter has a meaningful description.
• Each new command has a test.

(see Authoring Command Modules)

[tjprescott]

This PR is being opened now for review. It will not pass CI and thus cannot be merged. The work was done based on a draft azure-mgmt-network Python SDK that hasn't been published yet. Additionally, should Azure/azure-rest-api-specs#1494 be merged soon, I will need a new azure-mgmt-storage SDK published.

[codecov-io]

Codecov Report

Merging #4269 into master will increase coverage by 0.02%.
The diff coverage is 83.16%.

@@            Coverage Diff             @@
##           master    #4269      +/-   ##
==========================================
+ Coverage   70.12%   70.15%   +0.02%     
==========================================
  Files         475      475              
  Lines       29692    29769      +77     
  Branches     4556     4575      +19     
==========================================
+ Hits        20822    20883      +61     
- Misses       7426     7434       +8     
- Partials     1444     1452       +8

Impacted Files	Coverage Δ
.../azure-cli-core/azure/cli/core/profiles/_shared.py	88.18% <ø> (ø)	⬆️
src/azure-cli-core/azure/cli/core/commands/arm.py	83.3% <0%> (-0.31%)	⬇️
...twork/azure/cli/command_modules/network/_params.py	93.42% <100%> (ø)	⬆️
...work/azure/cli/command_modules/network/commands.py	94.35% <100%> (ø)	⬆️
...ure/cli/command_modules/network/_client_factory.py	84.61% <100%> (+1.28%)	⬆️
...orage/azure/cli/command_modules/storage/_params.py	87.08% <100%> (+0.24%)	⬆️
...network/azure/cli/command_modules/network/_help.py	100% <100%> (ø)	⬆️
...storage/azure/cli/command_modules/storage/_help.py	100% <100%> (ø)	⬆️
...etwork/azure/cli/command_modules/network/custom.py	62.46% <100%> (+0.32%)	⬆️
...rage/azure/cli/command_modules/storage/commands.py	97.07% <75%> (-1.12%)	⬇️
... and 4 more

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