Install jq tool in elastic-agent container to parse ES output

[ChrsMark]

What does this PR do?

Tests for elastic-agent were failing because of:

(23) Failed writing body
/etc/writer.sh: 12: jq: not found
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100 13884  100 13884    0     0  1129k      0 --:--:-- --:--:-- --:--:-- 1129k
curl: (23) Failed writing body (0 != 13884)

Closes #1992

[mergify]

This pull request does not have a backport label. Could you fix it @ChrsMark? 🙏
To fixup this pull request, you need to add the backport labels for the needed
branches, such as:

• backport-v./d./d./d is the label to automatically backport to the 7./d branch. /d is the digit
  NOTE: backport-skip has been added to this pull request.

[elasticmachine]

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• Start Time: 2022-02-11T10:57:56.352+0000

• Duration: 49 min 11 sec

Test stats 🧪

Test	Results
Failed	0
Passed	253
Skipped	0
Total	253

💚 Flaky test report

Tests succeeded.

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[mdelapenya]

Thank you @ChrsMark for your time debugging this issue! Merged and backported to the maintenance branches