Introducing RequiredFileNamePatterns feature to read files depending on the existence of other files

[olhepp-avintis]

Purpose

The purpose of this pull request is to introduce a feature covering a common use case, which is reading a file depending of the existence of another file.

Release note

Added RequiredFileNamePatterns feature to process files depending on the existence of other files using regular expressions.

Documentation

Example for usage:

<parameter name="transport.vfs.FileNamePattern">(.*)[.](hl7|pdf)$</parameter>
<parameter name="transport.vfs.RequiredFileNamePatterns">$1[.]pdf,$1[.]hl7</parameter>

The above mentioned example shows that a file (with .hl7 or .pdf extension) is only transfered, if both regular expression defined in the “RequiredFileNamePattern” are satisfied.
The $1 part represents the first group (parentheses) of the FileNamePattern property.
Processing files will be processed in the order of their appearance in RequiredFileNamePatterns parameter.

[CLAassistant]

All committers have signed the CLA.

[arunans23]

Thank you for your contribution. Can you sign the CLA to merge the PR?

[arunans23]

Shall we format the code segments? It seems both tabs and spaces are used. Let's use only spaces and format the code. Please check other places as well.

[arunans23]

Shall we explain in the PR description a little bit more about why this requirement came up?