Pull request: 3020 runtime clients sources control

Merge in DNS/adguard-home from 3020-client-sources to master

Closes #3020.

Squashed commit of the following:

commit f8e6b6d63373f99b52f7b8c32f4242c453daf1a4
Merge: 41fb071d 0a1ff65b
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Apr 25 19:19:15 2022 +0300

    Merge branch 'master' into 3020-client-sources

commit 41fb071deb2a87e0a69d09c8f418a016b4dd7e93
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Apr 25 13:38:28 2022 +0300

    home: fix nil, imp docs

commit aaa7765914a8a4645eba357cd088a9470611ffdc
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Mon Apr 25 12:25:47 2022 +0300

    home: imp code

commit 3f71b999564c604583b46313d29f5b70cf51ee14
Author: Eugene Burkov <E.Burkov@AdGuard.COM>
Date:   Fri Apr 22 19:12:27 2022 +0300

    home: runtime clients sources control

CHANGELOG.md

@@ -23,6 +23,8 @@ and this project adheres to
 
 ### Added
 
+- The ability to control each source of runtime clients separately via
+  `clients.runtime_sources` configuration object ([#3020]).
 - The ability to customize the set of networks that are considered private
   through the new `dns.private_networks` property in the configuration file
   ([#3142]).
@@ -63,8 +65,36 @@ and this project adheres to
 
 #### Configuration Changes
 
-In this release, the schema version has changed from 12 to 13.
+In this release, the schema version has changed from 12 to 14.
 
+- Object `clients`, which in schema versions 13 and earlier was an array of
+  actual persistent clients, is now consist of `persistent` and
+  `runtime_sources` properties:
+
+  ```yaml
+  # BEFORE:
+  'clients':
+  - name: client-name
+    # …
+
+  # AFTER:
+  'clients':
+    'persistent':
+      - name: client-name
+        # …
+    'runtime_sources':
+      whois: true
+      arp: true
+      rdns: true
+      dhcp: true
+      hosts: true
+  ```
+
+  The value for `clients.runtime_sources.rdns` field is taken from
+  `dns.resolve_clients` property.  To rollback this change, remove the
+  `runtime_sources` property, move the contents of `persistent` into the
+  `clients` itself, the value of `clients.runtime_sources.rdns` into the
+  `dns.resolve_clietns`, and change the `schema_version` back to `13`.
 - Property `local_domain_name`, which in schema versions 12 and earlier used to
   be a part of the `dns` object, is now a part of the `dhcp` object:
 
@@ -85,6 +115,9 @@ In this release, the schema version has changed from 12 to 13.
 
 ### Deprecated
 
+- The `--no-etc-hosts` option.  Its' functionality is now controlled by
+  `clients.runtime_sources.hosts` configuration property.  v0.109.0 will remove
+  the flag completely.
 - Go 1.17 support.  v0.109.0 will require at least Go 1.18 to build.
 
 ### Fixed
@@ -94,6 +127,7 @@ In this release, the schema version has changed from 12 to 13.
 
 [#1730]: https://github.com/AdguardTeam/AdGuardHome/issues/1730
 [#2993]: https://github.com/AdguardTeam/AdGuardHome/issues/2993
+[#3020]: https://github.com/AdguardTeam/AdGuardHome/issues/3020
 [#3057]: https://github.com/AdguardTeam/AdGuardHome/issues/3057
 [#3142]: https://github.com/AdguardTeam/AdGuardHome/issues/3142
 [#3157]: https://github.com/AdguardTeam/AdGuardHome/issues/3157