text: Title: [FEATURE] Corpus for input values
  Body: ### Is your feature request related to a problem? Please describe
  
  Sometimes the user wants to test a large set of specific values to ensure corner cases are always covered.
  
  ### Describe the solution you'd like
  
  A way to load such a corpus conveniently. The corpus format is not yet clear but at first glance, it could be done on the Open API parameters basis, i.e. they are named so it could be just a mapping `param => [variant_A, variant_B, ...]`. It would also correspond to a CSV file structure, where each column will have values for each parameter.
  
  However, it is unclear how to deal with other parameters, e.g. inside `components` - the user may want to cover some specific properties of objects nested inside `components`.
  
  Possible Python API:
  
  ```python
  from schemathesis.corpus import Entry
  
  
  schema.corpus.add(
      Entry.from_path(
          path="#/components/User/name",
          values=["a", "b", "c"],
          filter=...  # Use values only in some specific API operation
      ),
      Entry.named(
          # All `user_id` parameters
          name="user_id",
          values=["42", "43", "44"]
      ),
  )
  ```
  
  CLI:
  
  ```
  st run --corpus-path=...
  ```
  
  However, it is unclear how such a file should be structured.
  
  ### Describe alternatives you've considered
  
  Currently, it is not super convenient to do so. The closest equivalent is the `add_examples` hook, but it requires constructing examples manually. Alternatively, the user may modify their API schema which is not feasible for a large set of values.
  
  ### Additional context
  
  Discussed privately in Discord - maybe JMeter's input values could be a source of inspiration for this.
  