Bluetooth: Host: Add LE Power Control Request Procedure APIs

This commits adds the LE API's for the LE Power Control Request Feature
in Zephyr.

The support of feature is provided with the controller-based feature
selection with BT_CTLR_LE_POWER_CONTROL_SUPPORT and is selectable via
BT_TRANSMIT_POWER_CONTROL.

With the new APIs, the applications will:
get improved reading of local and remote tx power
be aware of changes in remote or local tx power

Defined HCI commands in Core Spec v5.4:
7.8.117 LE Enhanced Read Transmit Power Level command:
improvement to existing local tx power reading.
7.8.118 LE Read Remote Transmit Power Level command:
Remote tx power is read through an event (LE Transmit Power Reporting)
7.8.121 LE Set Transmit Power Reporting Enable command:
Enables local or remote tx power reporting to monitor changes in tx power
7.7.65.33 LE Transmit Power Reporting event

Note: to utilize the Feature fully Nordic-LL-only vendor-specific commands
are needed. These will not be added in RTOS zephyr but instead
implemented in a maintainable way in sdk.

Signed-off-by: Kyra Lengfeld <kyra.lengfeld@nordicsemi.no>