always enable cors middleware, even on failing requests

[Andrew7234]

Original issue description:

Return CORS headers on failed API responses

When API response fails it doesn't include Access-Control-Allow-Origin header. So frontend isn't allowed to even read the error code. e.g. after

- GET https://testnet.nexus.oasis.io/v1/consensus/accounts/oasis1qrtyn2q78jv6plrmexrsrv4dh89wv4n49udtg2km/debonding_delegations?limit=5&offset=0 net::ERR_FAILED 502 (Bad Gateway) 
- Frontend only knows TypeError: Failed to fetch  
- (browser has more access than javascript and it prints to console
Access to XMLHttpRequest at 'https://testnet.nexus.oasis.io/v1/consensus/accounts/oasis1qrtyn2q78jv6plrmexrsrv4dh89wv4n49udtg2km/debonding_delegations?limit=5&offset=0' from origin 'http://localhost:1234' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.)

To reproduce after debonding_delegations endpoint is fixed:
- open https://explorer.oasis.io/
- browser console
- console.log('aaa', (await fetch('https://testnet.nexus.oasis.io/v1/consensus/accounts/oasis1qrtyn2q78jv6plrmexrsrv4dh89wv4n49udtg1km')).status)  
- does not print "aaa 400"

CORS headers were not returned for failing/malformed requests; this PR fixes that by manually running the CORS middleware.

» curl -i -H 'Origin: example.com' 'localhost:8008/v1/consensus/accounts/oasis1qrtyn2q78jv6plrmexrsrv4dh89wv4n49udtg1k'
HTTP/1.1 400 Bad Request
Access-Control-Allow-Origin: *
Content-Type: application/json; charset=utf-8
Vary: Origin
X-Content-Type-Options: nosniff
Date: Wed, 31 Jul 2024 22:20:53 GMT
Content-Length: 227

{"msg":"Invalid format for parameter address: error unmarshalling 'oasis1qrtyn2q78jv6plrmexrsrv4dh89wv4n49udtg1k' text as *api.Address: address: decoding from bech32 failed: decoding bech32 failed: invalid separator index 43"}

@lukaw3d please lmk if this isn't sufficient; I tried testing on browser but I wasn't able to see the cors headers at all, even for successful requests. (maybe bc of cloudflare?)

[lukaw3d]

In browser you have make request from a different origin e.g.

• open https://explorer.oasis.io/
• browser console
• console.log('aaa', (await fetch('https://testnet.nexus.oasis.io/v1/consensus/accounts/oasis1qrtyn2q78jv6plrmexrsrv4dh89wv4n49udtg1km')).status)
• look at request