[core] Created internal config storage for a socket

[ethouris]

What's changed:

1. All variables representing multiplexer-related options are moved to a separate class
2. All other options are moved to CSrtConfig class that derives from the one above
3. Multiplexer-related options are now in use when creating the multiplexer. Multiplexer contains this object instead of single fields for required options and it is used in the procedure of finding the existing multiplexer.
4. Options have setters assigned to an option as template parameter and they are dispatched by finding in the option array. The solution was generally done in order to be able to forward the call to the option directly in case when the option name is already known, which was not necessary, but the already crafted solution still reduced the complexity (array index and call a function by pointer replaced binary search for enum).
5. The restrictions are defined by flags and checked inside the socket setter function before accessing the option. Among the flags there are also options that require specific post-action in case when the option was set on the socket.
6. The new socket option setting function consists now of precondition check, option forwarding, and post-action.
7. The options of string type are represented by a hard-limited character array coming with a handy wrapper named StringStorage.

[maxsharabayko]

Might be worth applying clang-format on socketconfig.h and cpp

[maxsharabayko]

CI build failure

[maxsharabayko]

Follow up PRs/issues:

• [BUG] PRE restriction is not applied on a listener socket #1873 - bug: PRE restrictions are not applied on a listener socket, allowing to change latency, TSBPD mode etc. while listening for incoming connections.
• Fixed bug: wrong size setting for StringStorage. Added UT. #1841 - bug: wrong size setting for StringStorage;
• Removed 'm_' prefix in socket config structs #1839 - minor renaming: removing m_ prefix from struct members,
• [core] Fixed post-action for socket options #1820 - bug: missing post-action for socket options,
• [core][apps] Fixed restrictions for options and replication in the app array #1828 - bug: missing SRTO_BINDTODEVICE and wrong action qualifier in apps.
• [core] Fixed incorrect setting streamid in internal config in HS (last 4 characters) #1868 - bug: incorrect streamID length retrieved via srt_getsockopt.
• [core] Fixed incorrect setting streamid in internal config in HS (last 4 characters) #1868 - bug no2: accepted socket inherits StreamID from listener socket, but must not.
• Fix SRTO_CONNTIMEO restrict #1864 - changed POST restriction of SRTO_CONNTIMEO. Changed to PRE. SRT v1.4.2 had PRE.in the docs, but no restriction in code (aka POST).
• [BUG] SRTO_FC setter bug #1898 - bug SRTO_FC socket option setting is wrongfully limited to 32 packets. PR [core] Fixed wrong limitation on SRTO_FC option. Fixed documentation. #1899.