Improve formatting of config validation errors

[emontnemery]

Proposed change

Improve formatting of config validation errors:

With this PR:

Invalid config for [iot_domain.non_adr_0007] at configuration.yaml, line 7: expected str for dictionary value 'option1', got 123.
Invalid config for [iot_domain] at configuration.yaml, line 9: required key not provided 'platform', got None.
Invalid config for [adr_0007_2] at configuration.yaml, line 16: required key not provided 'adr_0007_2->host', got None.
Invalid config for [adr_0007_3] at configuration.yaml, line 21: expected int for dictionary value 'adr_0007_3->port', got 'foo'.

Without this PR:

Invalid config for [iot_domain.non_adr_0007] at configuration.yaml, line 7: expected str for dictionary value @ data['option1']. Got 123.",
Invalid config for [iot_domain] at configuration.yaml, line 9: required key not provided @ data['platform']. Got None.
Invalid config for [adr_0007_2] at configuration.yaml, line 16: required key not provided @ data['adr_0007_2']['host']. Got None.
Invalid config for [adr_0007_3] at configuration.yaml, line 21: expected int for dictionary value @ data['adr_0007_3']['port']. Got 'foo'.

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
• New integration (thank you!)
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• Deprecation (breaking change to happen in the future)
• Breaking change (fix/feature causing existing functionality to break)
• Code quality improvements to existing code or addition of tests

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• This PR fixes or closes issue: fixes #
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[home-assistant]

Hey there @PhracturedBlue, @tetienne, @home-assistant/core, mind taking a look at this pull request as it has been labeled with an integration (template) you are listed as a code owner for? Thanks!

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[emontnemery]

Note: This PR will need to be rebased once #103959 is merged

[MartinHjelmare]

Do you have a preferred order of merging of these PRs?

[MartinHjelmare]

Suggested change

	output = Exception.__str__(ex)
	output = str(ex)

[emontnemery]

That won't work because this function is meant as an alternative to the stringification done by vol.Invalid.__str__. I'll add a comment explaining this.

[MartinHjelmare]

We'll explain this further in a follow up.

[home-assistant]

Please take a look at the requested changes, and use the Ready for review button when you are done, thanks 👍

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[emontnemery]

Do you have a preferred order of merging of these PRs?

Yes, I want to merge #103959 before this one. PR #103955 is also related, but should not cause any conflicts.