Namespace (and possibly spec) HS_DISABLED error code

[Half-Shot]

As per matrix-org/matrix-react-sdk#5576 (comment)

I'm mindful to namespace it now, as I don't think we make any assurances that random unspecced strings must remain the same.

[Half-Shot]

Turns out that the error response

synapse/synapse/api/errors.py

Line 320 in f31f8e6

class ResourceLimitError(SynapseError):

is also not specified.

[anoadragon453]

This was added back in v1.7.2: #6173

Indeed, it should probably be namespaced or specced, just as monthly_active_user currently is. HS_DISABLED sounds rather homeserver agnostic, so I'd probably advocate for the latter.

[anoadragon453]

Err, wait M_RESOURCE_LIMIT_EXCEEDED at least is specced: https://matrix.org/docs/spec/client_server/r0.6.1#api-standards

[Half-Shot]

The string M_RESOURCE_LIMIT_EXCEEDED, but the spec writer neglected to include the additional keys in the error body.