allow READONLY&READWRITE only after CLIENT CAPA REDIRECT for standalone mode

[soloestoy]

fixes #1348

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.77%. Comparing base (653d5f7) to head (c87b50f).

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #1351      +/-   ##
============================================
+ Coverage     70.63%   70.77%   +0.14%     
============================================
  Files           116      116              
  Lines         63303    63307       +4     
============================================
+ Hits          44711    44803      +92     
+ Misses        18592    18504      -88     

Files with missing lines	Coverage Δ
src/cluster.c	88.57% <100.00%> (+0.06%)	⬆️

... and 15 files with indirect coverage changes

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[zuiderkwast]

I'm not sure we should fix this. See the discussion in #1348.

[zuiderkwast]

I'm convinced we should do this fix, especially for compatibility with other databases (kvrocks, keydb, who knows). Many clients support not only Valkey.

Only one comment is about the error message.

[zuiderkwast]

These very long error messages that include the full documentation are not my favourite style.

If you (a user) get an error, you would normally go to the documentation for the READONLY command and find out what it means.

A more concise way is to say that READONLY is allowed only if redirects are enabled. This includes cluster (always) and standalone (with client capa redirect).

Suggested change

	addReplyError(c, "This instance has cluster support disabled,"
	" you need to execute the CLIENT CAPA REDIRECT command,"
	" before you can use the READONLY command in standalone mode.");
	addReplyError(c, "Redirects are not enabled");

[soloestoy]

especially for compatibility with other databases (kvrocks, keydb, who knows).

I think the order is reversed, they should be compatible with us, not the other way around, haha.

[zuiderkwast]

especially for compatibility with other databases (kvrocks, keydb, who knows).

I think the order is reversed, they should be compatible with us, not the other way around, haha.

Yes, we can think that we are the best and greatest, but this is like Redis style thinking. I don't want to think in this way.