Accept fleet.proxy_url policy options

[michalpristas]

What does this PR do?

This PR reloads proxy settings and takes these settings into account when comparing clients.

Why is it important?

When proxy settings come as part of policy they are ignored because

• we do not set them at all
• they are not evaluated when comparing client.

First one is self explanatory. second one means that even though we change proxy for a fleet server host, it is not applied because we don't look at proxy settings when comparing clients. when clients are considered equal we do not reload them and keep using old one.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool

UT is difficult to add as this relies on pings of new fleet server. Suitable for new Integration test framework

Fixes: #1728

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• Start Time: 2023-01-25T10:12:10.512+0000

• Duration: 17 min 16 sec

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Test	Results
Failed	0
Passed	4849
Skipped	13
Total	4862

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	98.305% (58/59)	👍
Files	69.268% (142/205)	👍
Classes	69.231% (270/390)	👍
Methods	54.047% (828/1532)	👍
Lines	39.264% (9042/23029)	👎 -0.026
Conditionals	100.0% (0/0)	💚

[blakerouse]

Looks good.

I do think we need to have unit tests to cover this method as its getting more complex.