Use included SQL files instead of those included in etn

[PietrH]

I accidentally introduced a circular dependency, etnservice was dependent on etn and visa versa. While etnservice should be standalone. It used some sql files included in inst, now these are included in etnservice.

This PR includes a change to connect_to_etn() in an attempt to return a better error when something goes wrong when connecting to the database (eg. wrong credentials).

Todo

• Pass R CMD Check
• Resolve merge conflict
• Pass unit tests with {etn} uninstalled
• test error for connect_to_etn()
• check test coverage

Failing tests

Failing tests: are they covered in etn ? -> This PR is pre sync between etn main and etnservice, thus some failing tests/functions might have changed in the meantime. To avoid duplication of effort, it'll be more practical to solve these failing tests in a seperate PR. I've created issues and added skip()'s for them.

Failure (test-get_acoustic_detections.R:36:3): get_acoustic_detections() returns unique detection_id
nrow(df) not equal to nrow(df %>% distinct(detection_id)).
1/1 mismatches
[1] 100 - 42 == 58

Failure (test-list_receiver_ids.R:11:3): list_receiver_ids() returns unique list of values
all(!is.na(vector)) is not TRUE

`actual`:   FALSE
`expected`: TRUE 

[PietrH]

test coverage for utils is low, need to merge some tests from etn v2.3 into etnservice: #53