MAINT: Update MAST registry link and example doc

[tsdower]

Issue 3404 notes a MAST registry service used in astroquery's conesearch validation module has moved. This updates the links in code and documentation in order to save user confusion and network hops.

I ran some tests including validate.check_conesearch_sites() and affirmed the output is not substantively different from the existing .rst file examples, and that the new URL appears as expected. The .rst files could be updated further for current state-of-registry output, but as mentioned in the issue comments, this module is in the medium term intended to go away, so I stopped here for now.

Test output:

...astroquery_tests.py 
Downloading https://mast.stsci.edu/vo-tap/api/v0.1/registry/sync?lang=ADQL&query=SELECT%20*%20FROM%20rr.capability%20NATURAL%20JOIN%20rr.interface%20NATURAL%20JOIN%20rr.resource%20NATURAL%20JOIN%20rr.res_subject%20WHERE%20standard_id%20like%20%27ivo://ivoa.net/std/conesearch%%27AND%20intf_type=%27vs:paramhttp%27 [Done]
INFO: Only 19/23349 site(s) are validated [astroquery.vo_conesearch.validator.validate]
WARNING: SR=0.11451621372724685 is too large, using SR=0.1 for ivo://cds.vizier/i/220,4 [astroquery.vo_conesearch.validator.tstquery]
WARNING: SR=0.11451621372724685 is too large, using SR=0.1 for ivo://cds.vizier/i/243,4 [astroquery.vo_conesearch.validator.tstquery]
WARNING: SR=0.11451621372724685 is too large, using SR=0.1 for ivo://cds.vizier/i/252,4 [astroquery.vo_conesearch.validator.tstquery]
WARNING: SR=0.11451621372724685 is too large, using SR=0.1 for ivo://cds.vizier/i/255,4 [astroquery.vo_conesearch.validator.tstquery]
WARNING: 10 not found in registry! Skipped:
        http://astrometry.mit.edu/cgi-bin/vo_cone6.cgi?CAT=USNO-B1&
        http://wfaudata.roe.ac.uk/sdssdr8-dsa/DirectCone?DSACAT=SDSS_DR8&DSATAB=PhotoObjAll&
        http://astrometry.mit.edu/cgi-bin/vo_cone6.cgi?CAT=USNO-A2&
        http://wfaudata.roe.ac.uk/twomass-dsa/DirectCone?DSACAT=TWOMASS&DSATAB=twomass_xsc&
        http://wfaudata.roe.ac.uk/sdssdr7-dsa/DirectCone?DSACAT=SDSS_DR7&DSATAB=Star&
        http://wfaudata.roe.ac.uk/sdssdr8-dsa/DirectCone?DSACAT=SDSS_DR8&DSATAB=SpecObjAll&
        http://wfaudata.roe.ac.uk/sdssdr7-dsa/DirectCone?DSACAT=SDSS_DR7&DSATAB=Galaxy&
        http://wfaudata.roe.ac.uk/twomass-dsa/DirectCone?DSACAT=TWOMASS&DSATAB=twomass_psc&
        http://wfaudata.roe.ac.uk/sdssdr7-dsa/DirectCone?DSACAT=SDSS_DR7&DSATAB=PhotoObj&
        http://wfaudata.roe.ac.uk/sdssdr7-dsa/DirectCone?DSACAT=SDSS_DR7&DSATAB=PhotoObjAll&
 [astroquery.vo_conesearch.validator.validate]
Downloading https://mast.stsci.edu/vo-tap/api/v0.1/registry/sync?lang=ADQL&query=SELECT%20*%20FROM%20rr.capability%20NATURAL%20JOIN%20rr.interface%20NATURAL%20JOIN%20rr.resource%20NATURAL%20JOIN%20rr.res_subject%20WHERE%20standard_id%20like%20%27ivo://ivoa.net/std/conesearch%%27AND%20intf_type=%27vs:paramhttp%27
...

closes #3404

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 70.51%. Comparing base (52b94d7) to head (fe41cba).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
astroquery/vo_conesearch/validator/tstquery.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3406   +/-   ##
=======================================
  Coverage   70.51%   70.51%           
=======================================
  Files         232      232           
  Lines       19997    19997           
=======================================
  Hits        14100    14100           
  Misses       5897     5897           

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[bsipocz]

Thanks!