Prevent creation of bed with the same name

[iamsdas]

Prevent the creation of a bed, if a bed with the same name exists in that location.
Fixes: #2282

[vigneshhari]

This validation should be written in the validate method, these validations can also be written at the model level which might make more sense.

[iamsdas]

@vigneshhari
I updated the PR to add the validations in the model level (using the clean method) and made some minor changes so that DRF can handle these Django validation errors.

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[vigneshhari]

resolve the conflicts and we are good to merge.