Fix the attica pkgconfig file.

Summary: the file was unusable due to bogus version name, missing dependencies and wrong paths.

Test Plan:
Before:

```
  prefix=/data/kde/inst
  exec_prefix=/data/kde/inst/bin
  libdir=lib64
  includedir=include/KF5Attica

  Name: libKF5Attica
  Description: Qt library to access Open Collaboration Services
  #Requires:
  Version: ..
  Libs: -Llib64 -lKF5Attica
  Cflags: -Iinclude/KF5Attica
```

After:

```
prefix=/data/kde/inst
exec_prefix=${prefix}
libdir=/data/kde/inst/lib64
includedir=/data/kde/inst/include

Name: libKF5Attica
Description: Qt library to access Open Collaboration Services
URL: https://www.kde.org
Requires: Qt5Core Qt5Network
Version: 5.61.0
Libs: -L/data/kde/inst/lib64 -lKF5Attica
Cflags: -I/data/kde/inst/include/KF5/Attica
```

Subscribers: leinir, fvogt, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D23029