Add custom user-agent header to identify MVG

[pavradev]

Description

Right now it is hard to identify MVG usage since there is User-Agent header specified. This PR fixes this. Please read more in the issue desciption.

Fixes #218

Type of Change

• [ ] Bug fix (non-breaking change which fixes an issue -> bump patch)
• [ ] New feature (non-breaking change which adds functionality -> bump minor version)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected -> bump major version)
• [ ] Documentation Update
• [ ] CI/CD workflows Update

Checklist

• [ ] I have added tests that prove that my fix/feature works
• [ ] Linters pass locally and I have followed PEP8 code style
• [ ] New and existing tests pass locally
• [ ] I have updated the documentation if needed
• [ ] I have commented hard-to-understand areas in the code

Requirements

• [x] I have updated the MVG version

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: +1.28 :tada:

Comparison is base (eabb01d) 74.00% compared to head (9d81491) 75.28%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #219 +/- ## ========================================== + Coverage 74.00% 75.28% +1.28% ========================================== Files 12 12 Lines 954 955 +1 ========================================== + Hits 706 719 +13 + Misses 248 236 -12 ``` | [Impacted Files](https://app.codecov.io/gh/vikinganalytics/mvg/pull/219?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vikinganalytics) | Coverage Δ | | |---|---|---| | [mvg/http\_client.py](https://app.codecov.io/gh/vikinganalytics/mvg/pull/219?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vikinganalytics#diff-bXZnL2h0dHBfY2xpZW50LnB5) | `97.14% <100.00%> (+0.08%)` | :arrow_up: | | [mvg/mvg.py](https://app.codecov.io/gh/vikinganalytics/mvg/pull/219?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vikinganalytics#diff-bXZnL212Zy5weQ==) | `90.80% <100.00%> (+1.67%)` | :arrow_up: | ... and [1 file with indirect coverage changes](https://app.codecov.io/gh/vikinganalytics/mvg/pull/219/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=vikinganalytics)

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