Switch backend to redisearch to enable more search options

[mariobehling]

It was stated by Areeb in the past that we need to switch to redisearch in order to have more options for search. Please implement it and ensure search on the frontend works as expected.

Compare fossasia/open-event-frontend#6119

[namanjain007]

working on it .

[sudhanshu456]

@namanjain007 are you still working on it? If not I will pick it up.

[norbusan]

This looks like a serious project. As far as I see there is code for using ElasticSearch for searching, but we don't deploy with elasticsearch. Not sure where/how search then is performed at all.

Also, simple upgrading the redis container to the redis-stack to get the redisearch might not be enough, because all events need to be indexed.

Code changes are that new data needs to be indexed, too.

Looks like a bigger project to me