[RHELC-1507] Port environment variables to config file

[r0x0d]

This patch introduces the initial work to port the environment variables to be read by a configuration file, parsed, and put into the ToolOpts class.

With that, we are aiming to remove the environments variables completely in the next release, managing all the configurations/inhibitors/settings through that config file.

Jira Issues:

• RHELC-1507

Checklist

• [ ] PR has been tested manually in a VM (either author or reviewer)
• [ ] Jira issue has been made public if possible
• [ ] [RHELC-] or [HMS-] is part of the PR title
• [ ] GitHub label has been added to help with Release notes
• [ ] PR title explains the change from the user's point of view
• [ ] Code and tests are documented properly
• [ ] The commits are squashed to as few commits as possible (without losing data)
• [ ] When merged: Jira issue has been updated to Release Pending if relevant

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 91.48936% with 4 lines in your changes missing coverage. Please review.

Project coverage is 95.87%. Comparing base (9c4e6c0) to head (66e7744).

:exclamation: Current head 66e7744 differs from pull request most recent head a7904cf

Please upload reports for the commit a7904cf to get more accurate results.

Files	Patch %	Lines
convert2rhel/toolopts.py	91.48%	2 Missing and 2 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1272 +/- ## ========================================== + Coverage 95.83% 95.87% +0.03% ========================================== Files 55 55 Lines 4756 4774 +18 Branches 836 833 -3 ========================================== + Hits 4558 4577 +19 Misses 112 112 + Partials 86 85 -1 ``` | [Flag](https://app.codecov.io/gh/oamg/convert2rhel/pull/1272/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | Coverage Δ | | |---|---|---| | [centos-linux-7](https://app.codecov.io/gh/oamg/convert2rhel/pull/1272/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `91.07% <91.48%> (+0.05%)` | :arrow_up: | | [centos-linux-8](https://app.codecov.io/gh/oamg/convert2rhel/pull/1272/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `92.00% <91.48%> (+0.05%)` | :arrow_up: | | [centos-linux-9](https://app.codecov.io/gh/oamg/convert2rhel/pull/1272/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `92.05% <91.48%> (+0.05%)` | :arrow_up: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg#carryforward-flags-in-the-pull-request-comment) to find out more.

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