LICENSES: Add the Apache-2.0 license for standalone files

LICENSES: Add the Apache-2.0 license for standalone files

Add the full text of the Apache-2.0 license to the OpenOCD tree.
It has the same content from:

  https://spdx.org/licenses/Apache-2.0.html#licenseText

but reformatted as in the Linux kernel document and added the
required tags for reference and tooling.
While this commit is specific for standalone files, it already
reports the information for dual licensing.

Change-Id: I1fd427256c310ab733fb5d50f344ac52c64a56f5
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/8005
Tested-by: jenkins
Reviewed-by: Erhan Kurubas <erhan.kurubas@espressif.com>