Update git submodules

Update git submodules

* Update docs/submodules/ccsdk/apps.git from branch 'master'
  to a0f6c597b54f42e141be6f41c6b228f4dc3ee988
  - Merge "Adding custom headers capability to REST client"
  - Adding custom headers capability to REST client

    For YANG PATCH requests to ODL to work, they need to have a Content-
    type header of application/yang.patch+json and should not have Accept
    as application/json

    Current REST client inserts a default header to the requests with this
    content:

      Content-Type: application/json
      Accept: application/json

    The solution was to add the possibility of sending custom headers alon-
    gside the other parameters.

    Change-Id: I2cf0cd2ef7b87f4f5a246d427dffafe266cb33f7
    Issue-ID: CCSDK-926
    Signed-off-by: ottero <rodrigo.ottero@est.tech>