Optimized query when a dashboard_id is given (most of the time)
- Does not pull in the full list of KPIs anymore
- Uses a DB join instead

Added a helper for extracting pagination params from request.args.

Formatted file.

When the error is on the client, the status code should be 400

Also changed pagination_args to take the default value as parameters -
useful in debugging.

- formatted using black and isort
- fixed type errors
    - check the value returned by `get_json()` is None before using it
        - returns a message with 400 if it's not a JSON
- fixed flake8 errors
- fixed docstrings
- create a new logger for the alert view module instead of using the
  root logger (`current_app.logger`)
- reduced total errors and warnings from 60+ to 0

Added a new module `chaos_genius.utils.search` that has a helper
function that extracts the `query` arguments from URL parameters and
makes an SQL alchemy filter for the given column.

Used this in the list endpoint of KPI, kpi-dashboard, data source and
alert APIs.
- moved common filters to a list above the branches
- the search_filter is appended to it if present

Fixes bug in previous commit

frontend requirement

- formatted with black and isort
- added docstrings for all functions
- validate JSON before using it
- ignore blind except errors

Used globals to store the default and mapping in one place - adding a
new sort require change to one place only.

Added `sort_by` arg in the list endpoint. Validation is performed on it
too. The sorting is done by `get_dashboard_list` in the controller
instead of directly having it in the view.

Added missing docstring to `get_dashboard_list`.

The endpoints are:
- `/api/connection/used-types`: list of data source types currently in
  use
- `/api/dashboard/names`: list of all dashboard names
- `/api/alert/used-status-types`: list of all alert status types
- `/api/alert/used-channel-types`: list of all alert channel types
  currently in use

KPI list (`/api/kpi`):
- supports `dashboard_id` and `datasource_type` params
- Example:
  `http://localhost:5000/api/kpi?dashboard_id=1&datasource_type=Postgres`

Data source list (`/api/connection`):
- supports `datasource_type`
- Example: `http://localhost:5000/api/connection?datasource_type=Druid`

Alert list (`/api/alert`):
- supports `channel` and `active`
- Example: `http://localhost:5000/api/alert?channel=email&active=false`
- To consider `active` to be True, use `true`, `1`, or `True`
- This is not named `status` because that has a different meaning in the
  backend/DB model

Uses getlist [1] to take all values of the parameter instead of just the
first one. The query is changed to use `in_` instead of `==`.

Type conversions are applied to each element in the list as appropriate.
The `type` parameter of `getlist` is not used since it ignores values
that cannot be parsed to that type - we want to show an explicit error
instead.

[1]: https://werkzeug.palletsprojects.com/en/2.1.x/datastructures/#werkzeug.datastructures.MultiDict.getlist

…nius into feature/pagination-FE

Made changes to return the filter params are empty.

Now multiple values for a filter param can be sent
spererated by '&' or the values can be ',' separated
or a combination of both.

Inconsistencies were introduced in 79328ca

and added TODO for refactor in the future

The new logic to handle multiple filters given as comma separated values
and as multiple params added in 79328ca
was not added to the get-dashboard-list endpoint.

This commit adds it there too.