Add support for hiding and redacting sensitive details

[vlovgr]

Hiding sensitive details

• Change ConfigValue#toString and ConfigEntry#toString to not include values.
• Change Show instances for ConfigValue and ConfigEntry to not include values.
• Add ConfigValue#toStringWithValue and ConfigEntry#toStringWithValues for keeping the previous toString behaviours.

You'll no longer have to worry about accidentally logging values, unless you're explicitly logging the result from a function with value in the name (sourceValue, value, toStringWithValue, ...).

Redacting sensitive details

• Add ConfigError#sensitive for creating errors with sensitive details.
• Add ConfigError#redactSensitive for redacting sensitive details.
• Add ConfigError#redactedValue placeholder for redacted details.
• Add ConfigDecoder#redactSensitive for redacting sensitive details in decoding errors.
• Change ConfigDecoder[Secret[A]] to automatically redact sensitive details.
• Change ConfigError#combined, missingKey, readException, wrongType to redact sensitive details.

In effect, this means that if you're using Secret to wrap the types of your secret configuration values, sensitive details will now automatically be redacted in error messages. And you will not have to worry about ever accidentally including secret values in log output.

scala> env[Secret[Int]]("FILE_ENCODING")
     |  .orElse(prop("file.encoding"))
     |  .value.left.map(_.message)
res0: Either[String,ciris.Secret[Int]] = Left(Missing environment variable [FILE_ENCODING] and system property [file.encoding] with value [<redacted>] cannot be converted to type [Int])

[codecov]

Codecov Report

Merging #151 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #151      +/-   ##
==========================================
+ Coverage   99.71%   99.72%   +<.01%     
==========================================
  Files          43       43              
  Lines         704      717      +13     
  Branches        4        5       +1     
==========================================
+ Hits          702      715      +13     
  Misses          2        2

Impacted Files	Coverage Δ
...ore/shared/src/main/scala/ciris/ConfigSource.scala	100% <ø> (ø)	⬆️
...m/src/main/scala/ciris/CirisPlatformSpecific.scala	100% <ø> (ø)	⬆️
...ined/jvm/src/main/scala/ciris/refined/syntax.scala	100% <ø> (ø)	⬆️
...les/core/shared/src/main/scala/ciris/package.scala	100% <ø> (ø)	⬆️
...re/shared/src/main/scala/ciris/ConfigDecoder.scala	100% <100%> (ø)	⬆️
...core/shared/src/main/scala/ciris/ConfigValue.scala	100% <100%> (ø)	⬆️
...ain/scala/ciris/decoders/CirisConfigDecoders.scala	100% <100%> (ø)	⬆️
...n/scala/ciris/cats/api/CirisInstancesForCats.scala	100% <100%> (ø)	⬆️
...core/shared/src/main/scala/ciris/ConfigError.scala	100% <100%> (ø)	⬆️
...core/shared/src/main/scala/ciris/ConfigEntry.scala	100% <100%> (ø)	⬆️

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