Add docs on difference between OmegaConf and OmegaConfigLoader

[merelcht]

Description

Fixes #3247

Development notes

Added docs to address:

• Why is OmegaConf different to Kedro's ConfigLoader and when to use either one?

Added examples for:

• How to load a single file? plain OmegaConf.load
• How to load a data catalog when you have a credentials? Kedro OmegaConfigLoader
• How to load a data catalog when you have templating? Kedro OmegaConfigLoader

For reviewers

The thing I struggled with for these docs is where to put them. I've added them all to the configuration docs, but I'm not sure if it really fits here, because this is actually part of the whole story of using Kedro as a library vs Framework.

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Checklist

• Read the contributing guidelines
• Signed off each commit with a Developer Certificate of Origin (DCO)
• Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• Updated the documentation to reflect the code changes
• Added a description of this change in the RELEASE.md file
• Added tests to cover my changes
• Checked if this change will affect Kedro-Viz, and if so, communicated that with the Viz team

[stichbury]

Few minor changes to address Vale feedback and simplify the read but TBH all are suggestions and feel free to ignore some, all or none.

[astrojuanlu]

💯

[stichbury]

These are great, thank you. Two minor typo fixes (which also address a Vale moan) but approving as a fantastic job. Thanks for the updates 🌟