Allows to set custom properties on a teams client

[firefart]

Description

These changes allow so set the following parameters on the teams client:

• A custom Proxy URL (the plugin normally uses the ENV variables, but now you can also set it directly)
• A custom user agent for all outgoing requests to Teams
• A custom HTTP Client if you want to tweak even more properties

The methods are all accessible on the TeamsClient https://github.com/atc0005/go-teams-notify/blob/master/send.go

Motivation and Context

Setting a Proxy on outgoing requests without using env variables

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (no code change)
• Refactor (refactoring production code)
• Other

Checklist:

• My code follows the code style of this project.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 89 lines in your changes missing coverage. Please review.

Project coverage is 28.66%. Comparing base (8efdc15) to head (9f71118).
Report is 86 commits behind head on main.

Files with missing lines	Patch %	Lines
service/msteams/mock_teams_client.go	0.00%	78 Missing ⚠️
service/msteams/ms_teams.go	0.00%	11 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #927       +/-   ##
===========================================
- Coverage   74.10%   28.66%   -45.45%     
===========================================
  Files          44       61       +17     
  Lines        1572     2735     +1163     
===========================================
- Hits         1165      784      -381     
- Misses        307     1830     +1523     
- Partials      100      121       +21     

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[nikoksr]

Hi @firefart, thank you for the PR! Just a quick question, I'm not able to try this out rn, but wouldn't it be possible to set the proxy by using the SetHTTPClient() method you provided?

client := http.DefaultClient
client.Transport = &http.Transport{Proxy: http.ProxyURL(url)}

teamsSvc.SetHTTPClient(client)

Or does SetProxy() serve another purpose besides comfort that I'm missing? Because while I do enjoy the comfort this brings, it also leads to a commitment for us to add setter functions per field of mutable state. While v2 of the library is on the horizon, I'd still like to strike a balance between control and minimalism when it comes to the API of v1. SetHTTPClient() gives full control over the HTTP client while having minimal impact on the API's verbosity.

Let me know your thoughts on this, totally possible I'm just missing something. Cheers :)

[firefart]

Hi,
jeah I just wanted to set the proxy by hand and it's doable with the SetHTTPClient only too. I just exposed some methods that might be interesting to some users, but I'm also happy to just include SetHTTPClient