[RHELC-1286, RHELC-1555] Add tests validating the ELS support

[danmyway]

• add a full conversion test using the ELS repositories
• add non-destructive scenarios validating a correct repository enablement
• slightly modify the eus_support test

Jira Issues:

• RHELC-1286
• RHELC-1555

Checklist

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 95.42%. Comparing base (f784699) to head (dce500b). Report is 6 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1228 +/- ## ======================================= Coverage 95.42% 95.42% ======================================= Files 54 54 Lines 4699 4699 Branches 829 829 ======================================= Hits 4484 4484 Misses 132 132 Partials 83 83 ``` | [Flag](https://app.codecov.io/gh/oamg/convert2rhel/pull/1228/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/1228/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `90.63% <ø> (ø)` | | | [centos-linux-8](https://app.codecov.io/gh/oamg/convert2rhel/pull/1228/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `91.55% <ø> (ø)` | | | [centos-linux-9](https://app.codecov.io/gh/oamg/convert2rhel/pull/1228/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=oamg) | `91.61% <ø> (ø)` | | 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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[danmyway]

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[danmyway]

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[danmyway]

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