Initial IK seed

[SammyRamone]

This small PR adds an option to specify the initial IK seed.
It was helpful for my use case to be able to specify this, as I am using a high DoF robot and a difficult to reach workpiece.
Maybe it is helpful for others too. If you don't want to add this feature, it is also fine for me.
As long a this parameter is not defined, previous behavior of using the zero pose is used.
For the demo study, one can for example add the following to the optimization part of the config yaml (although it does not provide an advantage in this simple case).

  initial_seed:
    - name: joint_s
      position: 2.66
    - name: joint_l
      position: -1.54
    - name: joint_e
      position: -0.56
    - name: joint_u
      position: -2.20
    - name: joint_r
      position: -0.32
    - name: joint_b
      position: 1.81
    - name: joint_t
      position: 2.39

[marip8]

I think this is a reasonable addition. Would you mind adding this seed_state parameter to the unit test config file as an example for others as well?

[marip8]

Also, please run the .run-clang-format file to format your code additions

[SammyRamone]

Thanks for the feedback, I tried to implement the changes in the last commit.

[SammyRamone]

I worked in your suggestions. Sorry for taking to so long.

[marip8]

Looks good; thanks for the updates