CodeCoverage export - Improve error message

When you have a configuration error and the merge may not be finding the files, be more explicit about Where the files are expected.
```
ERROR: Found 0 code coverage file. Need at least two files to merge.
At /home/vsts/work/1/s/output/RequiredModules/Sampler/0.111.3/tasks/JaCoCo.coverage.build.ps1:157 char:13
+ throw "Found $($codecovFiles.Count) code coverage file. N …
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
At /home/vsts/work/1/s/output/RequiredModules/Sampler/0.111.3/tasks/JaCoCo.coverage.build.ps1:57 char:1
+ task Merge_CodeCoverage_Files {
```

Also, in the task "header" showing variables used for the run, be more descriptive about what is used where (`Code Coverage Output File` and `Code Coverage Merge Output File` and `Code Coverage File Pattern`...

```
Project Name = 'MyModule'
Source Path = '/home/vsts/work/1/s/source'
Output Directory = '/home/vsts/work/1/s/output'
Built Module Subdirectory = '/home/vsts/work/1/s/output/'
Module Manifest Path (src) = '/home/vsts/work/1/s/source/MyModule.psd1'
Versioned Output Directory = 'True'
Built Module Manifest = '/home/vsts/work/1/s/output/MyModule/3.3.0/MyModule.psd1'
Built Module Base = '/home/vsts/work/1/s/output/MyModule/3.3.0'
Module Version = '3.3.0-micy'
Module Version Folder = '3.3.0'
Pre-release Tag = 'micy'
Built Module Root Script = '/home/vsts/work/1/s/output/MyModule/3.3.0/MyModule.psm1'
Release Notes path = '/home/vsts/work/1/s/output/ReleaseNotes.md'

Pester Output Folder = '/home/vsts/work/1/s/output/testResults'
Code Coverage Threshold = '0.1'
Code Coverage Output File = /home/vsts/work/1/s/output/testResults/JaCoCo_coverage.xml
Code Coverage Merge Output File = /home/vsts/work/1/s/output/testResults/CodeCov_Merged.xml
Code Coverage File Pattern = Codecov*.xml
Merging Code Coverage Files = ''
```