Update Switch documentation for informatica and custom_etl

[yyoli-db]

What does this PR do?

Update switch documentation for https://github.com/databrickslabs/switch/pull/68

Relevant implementation details

Caveats/things to watch out for when reviewing:

Linked issues

Resolves #..

Functionality

• added relevant user documentation
• added new CLI command
• modified existing command: databricks labs lakebridge ...
• ... +add your own

Tests

• manually tested
• added unit tests
• added integration tests

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 66.44%. Comparing base (87c4e12) to head (e71210e).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2310   +/-   ##
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  Coverage   66.44%   66.44%           
=======================================
  Files          99       99           
  Lines        9090     9090           
  Branches      974      974           
=======================================
  Hits         6040     6040           
  Misses       2874     2874           
  Partials      176      176           

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[github-actions]

✅ 143/143 passed, 7 flaky, 5 skipped, 31m45s total

Flaky tests:

• 🤪 test_installs_and_runs_local_bladebridge (20.359s)
• 🤪 test_installs_and_runs_pypi_bladebridge (26.168s)
• 🤪 test_transpiles_informatica_to_sparksql_non_interactive[False] (18.703s)
• 🤪 test_transpile_teradata_sql_non_interactive[False] (20.187s)
• 🤪 test_transpile_teradata_sql_non_interactive[True] (22.644s)
• 🤪 test_transpile_teradata_sql (6.551s)
• 🤪 test_transpiles_informatica_to_sparksql_non_interactive[True] (3.848s)

_{Running from acceptance #3936}

[hiroyukinakazato-db]

I'm assuming users would replace the placeholders ({ADD_YOUR_CUSTOM_DEFINITION_HERE}, {ADD_YOUR_CUSTOM_INSTRUCTIONS_HERE}, {ADD_YOUR_CUSTOM_INPUT_HERE}, {ADD_YOUR_CUSTOM_OUTPUT_HERE}) with their own content? If so, it'd be good to mention that explicitly. The current wording just says to edit custom_etl.yml but doesn't call out which placeholders to replace.

[hiroyukinakazato-db]

Just to confirm: Could you share the reasoning behind replacing the PySpark ETL example with Informatica? I'm guessing it was to keep the number of examples manageable?