Combine both HowTo guides on mounting ceph storage?

[sfmig]

Is your feature request related to a problem? Please describe.
There is some repetition in both guides (which is expected since the goals are similar), but also some bits that show different ways of doing the same thing.

I wonder if this may be confusing? Having duplicate info is also prone to get "out of sync" with each other.

Describe the solution you'd like
Some options

• We could try making them more consistent.
• We could have one guide, and separate the two cases with sphinx-tabs.

Describe alternatives you've considered
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Additional context
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[niksirbi]

Agreed, combining makes sense here.