Use aiojobs for background tasks

[citramon]

What do these changes do?

Preparing for new release. Use aiojobs for background tasks.

Are there changes in behavior for the user?

nope

Related issue number

Resolvers: 536

Checklist

• [ ] I think the code is well written
• [ ] Unit tests for the changes exist
• [ ] Documentation reflects the changes
• [ ] Add a new news fragment into the CHANGES folder
  • name it <issue_id>.<type> (e.g. 588.bugfix)
  • if you don't have an issue_id change it to the pr id after creating the PR
  • ensure type is one of the following:
    • .feature: Signifying a new feature.
    • .bugfix: Signifying a bug fix.
    • .doc: Signifying a documentation improvement.
    • .removal: Signifying a deprecation or removal of public API.
    • .misc: A ticket has been closed, but it is not of interest to users.
  • Make sure to use full sentences with correct case and punctuation, for example: Fix issue with non-ascii contents in doctest text files.

[codecov[bot]]

Codecov Report

Merging #573 (46a197c) into master (760ccab) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #573   +/-   ##
=======================================
  Coverage   98.17%   98.17%           
=======================================
  Files          13       13           
  Lines        1040     1043    +3     
  Branches      140      140           
=======================================
+ Hits         1021     1024    +3     
  Misses         15       15           
  Partials        4        4           

Flag	Coverage Δ
unit	98.17% <100.00%> (+<0.01%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
aiocache/decorators.py	100.00% <100.00%> (ø)

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[citramon]

@Dreamsorcerer, this PR for preparing to new release from this TODO list. Could you check it?

[Dreamsorcerer]

Depends on #609.