Explicitly install pip3 for alpine based image

Desired Outcome

Alpine docker build should complete successfully after this PR is merged.

Current error: pip3: not found

 > [2/6] RUN apk update && apk upgrade && apk add bash && apk add python3 && pip3 install requests && pip3 install PTable:
#5 1.599 (2/10) Installing expat (2.4.8-r0)
#5 1.623 (3/10) Installing libffi (3.4.2-r1)
#5 1.635 (4/10) Installing gdbm (1.23-r0)
#5 1.647 (5/10) Installing xz-libs (5.2.5-r1)
#5 1.663 (6/10) Installing libgcc (11.2.1_git20220219-r2)
#5 1.676 (7/10) Installing libstdc++ (11.2.1_git20220219-r2)
#5 1.711 (8/10) Installing mpdecimal (2.5.1-r1)
#5 1.726 (9/10) Installing sqlite-libs (3.38.5-r0)
#5 1.749 (10/10) Installing python3 (3.10.5-r0)
pip3: not found
------
./DockerfileAlpine:2
--------------------
   1 |     FROM alpine:latest
   2 | >>> RUN apk update && apk upgrade && apk add bash && apk add python3 && pip3 install requests && pip3 install PTable
   3 |     RUN apk add git && git clone --recursive https://github.com/kubernetes-client/python.git && cd python/ && python3 setup.py install 
   4 |     RUN echo "alias kubiscan='python3 /KubiScan/KubiScan.py'" > /root/.bash_aliases && echo "alias kubiscan='python3 /KubiScan/KubiScan.py'" > /root/.bashrc
--------------------
ERROR: failed to solve: process "/bin/sh -c apk update && apk upgrade && apk add bash && apk add python3 && pip3 install requests && pip3 install PTable" did not complete successfully: exit code: 127

Implemented Changes

Added apk add cmd:pip3 in order to install pip3

Connected Issue/Story

Resolves https://github.com/alpinelinux/docker-alpine/issues/91

Definition of Done

At least 1 todo must be completed in the sections below for the PR to be merged.

Changelog

[ ] The CHANGELOG has been updated, or
[x] This PR does not include user-facing changes and doesn't require a CHANGELOG update

Test coverage

[ ] This PR includes new unit and integration tests to go with the code changes, or
[x] The changes in this PR do not require tests

Documentation

[ ] Docs (e.g. READMEs) were updated in this PR
[ ] A follow-up issue to update official docs has been filed here: [insert issue ID]()
[x] This PR does not require updating any documentation

Behavior

[ ] This PR changes product behavior and has been reviewed by a PO, or
[ ] These changes are part of a larger initiative that will be reviewed later, or
[x] No behavior was changed with this PR

Security

[ ] Security architect has reviewed the changes in this PR,
[ ] These changes are part of a larger initiative with a separate security review, or
[x] There are no security aspects to these changes

cyberark / KubiScan

Explicitly install pip3 for alpine based image #31