Clarify acceptable actions on a shared table along with expected patterns and add functional tests

[skliper]

Is your feature request related to a problem? Please describe.
Currently table sharing management requires careful design or restricting the design space to avoid block/priority concerns.

• There isn't a "read only" way to get a table address to restrict capability for management to a single "owner"
• Since update/management can be done by any app with shared access, blocking/priority has to be managed
• Not immediately clear how the locking/sharing is all intended to work together

Describe the solution you'd like
Should clarify the sharing design documentation, there's currently "hints" in the APIs and a very short section in the cFE Application Developer's Guide but there aren't functional tests that actually implement/exercise all the sharing patterns or a full description of how it's intended to work.

• Clearly describe how unregistering a shared table is expected to work (or not)
  

  cFE/modules/tbl/fsw/src/cfe_tbl_api.c

  Lines 655 to 658 in 82c1bd4

  	/* Remove the Access Descriptor Link from linked list */
  	/* NOTE: If this removes the last access link, then */
  	/* memory buffers are set free as well. */
  	CFE_TBL_RemoveAccessLink(TblHandle);

Describe alternatives you've considered
Consider additions/simplification to the sharing model like read only access, etc. Need to tie to requirements, funding, use cases, etc and trade against the additional complexity.

Additional context
Code review, see also #1509

Requester Info
Jacob Hageman - NASA/GSFC