COPDS-1777: custom ranking on catalogue search

[alex75]

This PR must be merget together with ecmwf-projects/cads-catalogue-api-service#79
In this PR:

• Added field 'popularity' on resources (integer from metadata.yaml, default 1)
• Added field 'fts' (ts_vector to consider lexemes from high_priority_terms)
• Added a new ranking function for FTS (ts_rank2)

[FussyDuck]

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