fix(datepicker): keep comp configuration updated (#5383)

[treeskar]

In this PR I made component's configuration to be always up to date.

Overview

Datepicker configuration composed with 4 parts:

1. _config: BsDatepickerConfig - default configuration
2. Input bsConfig: Partial - user can pass partial configuration, that can overwrite default one
3. Input bsValue: Date - datepicker value and also is part of config (config.value)
4. all other inputs, like: isDisabled, minDate, maxDate... - component's configuration properties, that user can tune separately.

We have to keep in mind, that any value that comes from Input can be changed any time.

Why issue happened

Configuration was recalculated (setConfig) only on ngOnInit() and on show() calls, therefore there are situations when calculated config was out of sync with updated input config properties.

Solution

I created config$ stream, that listens to every part of component's configuration and recalculates final config if any part updated . This way "_config" always reflects actual configuration state.

• read and followed the CONTRIBUTING.md guide.
• built and tested the changes locally.
• added/updated tests.
• added/updated API documentation.
• added/updated demos.

[codecov]

Codecov Report

Merging #5612 into development will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           development    #5612   +/-   ##
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  Coverage        52.52%   52.52%           
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  Files                3        3           
  Lines               99       99           
  Branches            17       17           
============================================
  Hits                52       52           
  Misses              37       37           
  Partials            10       10

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