Resolve NXCALS-7192 "Add instructions about lxplus"

Old page about access methods is split into:

https://nxcals-docs-rmucha.web.cern.ch/current/user-guide/data-access/access-methods/

https://nxcals-docs-rmucha.web.cern.ch/current/user-guide/python-environments/

https://nxcals-docs-rmucha.web.cern.ch/current/user-guide/using-spark-bundle/

https://nxcals-docs-rmucha.web.cern.ch/current/user-guide/using-lxplus/

Some improvements (I hope) to:

https://nxcals-docs-rmucha.web.cern.ch/current/user-guide/data-access/quickstart/

https://nxcals-docs-rmucha.web.cern.ch/current/user-guide/data-access/authentication/

https://nxcals-docs-rmucha.web.cern.ch/current/user-guide/swan/swan-session/

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@acc-logging-team - please have a look for approval.

Please describe the merge request here.

Closes NXCALS-7192