Added Catalog and Schema Mapping Instructions

[BesikiML]

Changes

What does this PR do?

Add instructions in the documentation on how to declare a catalog and define schema mappings using a custom configuration file.

Linked issues

Implemented: https://github.com/databrickslabs/bladerunner/issues/619

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.17%. Comparing base (6c56eb3) to head (2b3c34f).

Additional details and impacted files

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##             main    #2135   +/-   ##
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  Coverage   64.17%   64.17%           
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  Files          99       99           
  Lines        8364     8364           
  Branches      853      853           
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  Hits         5368     5368           
  Misses       2813     2813           
  Partials      183      183           

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[github-actions]

✅ 51/51 passed, 10 flaky, 3m29s total

Flaky tests:

• 🤪 test_validate_non_empty_tables (7ms)
• 🤪 test_validate_invalid_source_tech (172ms)
• 🤪 test_validate_table_not_found (1ms)
• 🤪 test_validate_successful_schema_check (299ms)
• 🤪 test_validate_invalid_schema_check (0s)
• 🤪 test_transpiles_informatica_to_sparksql (15.931s)
• 🤪 test_transpiles_informatica_to_sparksql_non_interactive[False] (15.141s)
• 🤪 test_transpile_teradata_sql_non_interactive[False] (17.554s)
• 🤪 test_transpiles_informatica_to_sparksql_non_interactive[True] (3.795s)
• 🤪 test_transpile_teradata_sql (19.798s)

_{Running from acceptance #2907}

[gueniai]

@BesikiML I think this should be part of the "Creating the custom configuration file" section, we can simply state the business intent as an example.
For example:
"So let's say you want to rename your tables or ensure they follow the UC three level namespace paradigm, you can do it as follows:"

and you add everything you have here