improve export filename

[kevinpapst]

Description

Will now consist of:

• a date prefix Ymd (example: 20211119)
• if query contained exactly 1 customer: dash + the customer name -customer
• if query contained exactly 1 project: dash + the project name -project
• if query contained exactly 1 user: dash + the user name -user

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• I verified that my code applies to the guidelines (composer code-check)
• I updated the documentation (see here)
• I agree that this code is used in Kimai and will be published under the MIT license

[codecov]

Codecov Report

Merging #2958 (ba31541) into master (56d0267) will increase coverage by 0.00%.
The diff coverage is 92.50%.

@@            Coverage Diff            @@
##             master    #2958   +/-   ##
=========================================
  Coverage     92.26%   92.26%           
- Complexity     7847     7858   +11     
=========================================
  Files           689      690    +1     
  Lines         24027    24063   +36     
=========================================
+ Hits          22168    22202   +34     
- Misses         1859     1861    +2     

Impacted Files	Coverage Δ
src/Export/Base/PDFRenderer.php	92.30% <50.00%> (-1.70%)	⬇️
src/Export/ExportFilename.php	96.96% <96.96%> (ø)
src/Export/Base/AbstractSpreadsheetRenderer.php	90.13% <100.00%> (+0.02%)	⬆️