Deprecate OwncloudClient - Helpers

[ZetaTom]

This is one of a series of pull requests which aim to replace all instances of OwnCloudClient with NextcloudClient. The reason for this change is that the newer NextcloudClient uses OkHttp, replacing the outdated Jackrabbit methods.

Specifically, this pull request implements the following:

• helper classes to ease the transition and refactoring
• general changes

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.

Project coverage is 48.85%. Comparing base (26dc847) to head (32a0006).

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1271      +/-   ##
============================================
- Coverage     48.94%   48.85%   -0.10%     
  Complexity      996      996              
============================================
  Files           206      208       +2     
  Lines          7835     7850      +15     
  Branches       1019     1019              
============================================
  Hits           3835     3835              
- Misses         3450     3465      +15     
  Partials        550      550              

Files	Coverage Δ
...c/main/java/com/nextcloud/operations/HeadMethod.kt	0.00% <0.00%> (ø)
.../main/java/com/nextcloud/common/JSONRequestBody.kt	0.00% <0.00%> (ø)

[github-actions]

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[github-actions]

SpotBugs

Category	Base	New
Bad practice	35	35
Correctness	34	34
Dodgy code	26	26
Internationalization	6	6
Malicious code vulnerability	49	49
Multithreaded correctness	3	3
Performance	8	8
Total	161	161

[github-actions]

SpotBugs

Category	Base	New
Bad practice	35	35
Correctness	34	34
Dodgy code	26	26
Internationalization	6	6
Malicious code vulnerability	49	49
Multithreaded correctness	3	3
Performance	8	8
Total	161	161

[github-actions]

SpotBugs

Category	Base	New
Bad practice	35	35
Correctness	34	34
Dodgy code	26	26
Internationalization	6	6
Malicious code vulnerability	49	49
Multithreaded correctness	3	3
Performance	8	8
Total	161	161

[github-actions]

SpotBugs

Category	Base	New
Bad practice	35	35
Correctness	34	34
Dodgy code	26	26
Internationalization	6	6
Malicious code vulnerability	49	49
Multithreaded correctness	3	3
Performance	8	8
Total	161	161

[github-actions]

SpotBugs

Category	Base	New
Bad practice	35	35
Correctness	34	34
Dodgy code	26	26
Internationalization	6	6
Malicious code vulnerability	49	49
Multithreaded correctness	3	3
Performance	8	8
Total	161	161