Support echo and prompt for an interactive option

[sakata1222]

PR for #802.

• If echo is true, just uses BufferedReader#readLine not Console#readPassword to read user input.
• If prompt is not empty, the specified string will be displayed to the end user for an interactive option.
• The default values:
  • echo : false
  • prompt : empty string

Here is the result of a sample class added by this PR. I use Windows 10.

PS C:\xxxxx\picocli> java -version
openjdk version "11.0.9.1" 2020-11-04
OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.9.1+1)
OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.9.1+1, mixed mode)

PS C:\xxxxx\picocli> java -cp "build/libs/picocli-4.5.3-SNAPSHOT.jar;picocli-examples/build/libs/picocli-examples.jar" picocli.examples.interactive.UserPasswordDemo "sample action"
Enter your user: dummy
Enter your password:
User: dummy, Password: secret
Action: sample action

[codecov-io]

Codecov Report

Merging #1284 (d767f5d) into master (a610c7c) will increase coverage by 0.01%.
The diff coverage is 85.45%.

@@             Coverage Diff              @@
##             master    #1284      +/-   ##
============================================
+ Coverage     93.82%   93.83%   +0.01%     
  Complexity      462      462              
============================================
  Files             2        2              
  Lines          6852     6882      +30     
  Branches       1842     1848       +6     
============================================
+ Hits           6429     6458      +29     
- Misses          138      141       +3     
+ Partials        285      283       -2     

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/picocli/CommandLine.java	93.66% <85.45%> (+0.01%)	318.00 <0.00> (ø)

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[remkop]

Merged.
Thank you for the contribution! This will be included in the 4.6 release.
(I still need to update the release notes.)