Enhance GitHub App local secrets handling

[smoy]

What changed?

• Prompt user regarding existing GitHub App secrets
• Remove local GitHub App secrets when setup is successful

Rationale

• We should not keep the local secrets when its successfully stored in SecretManager
• Explain to the user if there is local secrets for what org and what app

How was it tested?

If it was manually verified, list the instructions for your reviewers to follow.

• [ ] Unit Tests
• [ ] Functional Tests
• [x] Manually Verified

[codecov[bot]]

Codecov Report

Patch coverage has no change and project coverage change: -0.09% :warning:

Comparison is base (bec7490) 83.84% compared to head (72fee05) 83.75%. Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #559 +/- ## ========================================== - Coverage 83.84% 83.75% -0.09% ========================================== Files 105 105 Lines 12280 12287 +7 ========================================== - Hits 10296 10291 -5 - Misses 1984 1996 +12 ``` | Flag | Coverage Δ | | |---|---|---| | functional_tests | `65.96% <0.00%> (-0.14%)` | :arrow_down: | | functional_tests_config_discovery | `46.04% <0.00%> (+0.09%)` | :arrow_up: | | unit_tests | `74.01% <0.00%> (-0.05%)` | :arrow_down: | 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=noqdev#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files Changed](https://app.codecov.io/gh/noqdev/iambic/pull/559?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=noqdev) | Coverage Δ | | |---|---|---| | [iambic/plugins/v0\_1\_0/github/create\_github\_app.py](https://app.codecov.io/gh/noqdev/iambic/pull/559?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=noqdev#diff-aWFtYmljL3BsdWdpbnMvdjBfMV8wL2dpdGh1Yi9jcmVhdGVfZ2l0aHViX2FwcC5weQ==) | `0.00% <0.00%> (ø)` | | ... and [3 files with indirect coverage changes](https://app.codecov.io/gh/noqdev/iambic/pull/559/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=noqdev)

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