Implement server side location polygon search

[cpjmcquillan]

Implement polygon search in Algolia for locations where appropriate

For the relevant locations (as defined in TEVA-943 and #1682)insidePolygon search is carried out in Algolia.

For reference:

Vacancy.search('query', { insidePolygon: 'string of comma separated floats' })

Acceptance criteria

• Server side search (including job alerts) carries out location polygon searches where appropriate
• Code review

[bencmitchell]

https://dfedigital.atlassian.net/browse/TEVA-950