Setting up the default survey layer

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It would be good to have an option to set up the default survey layer. Currently, the default survey layer is defined:
- Based on the top editable vector layer in the layer panel
- The last layer edited by user

This gets complicated when you have a one-to-many relation and user edits two layers at the same time. E.g. you have have a parent point layer which you want to be your default survey layer. The layer is linked with a polygon (child layer). When user captures a point, then multiple polygons can be added. In this case, polygon layer becomes the survey layer when you next press record.

By having a default survey layer, we will make sure, always point layer in the above scenario will appear as the survey layer.

No files or tests are named. Start by tracing how the plugin chooses the survey layer when recording begins, then reproduce the parent-point and child-polygon one-to-many workflow described here. Done means users can configure a default survey layer and the chosen parent layer remains selected when recording again.

Written by the indexing model from the issue text.