Update some Case Studies mentioning Docker

[Babapool]

Fixes #31424

In this PR, small wording adjustments are made in the Case Studies that mention Docker. These changes include:

• Reword Docker containers to containers
• Reword Dockerize to containerize
• Reword Docker file to Dockerfile
• Changes just over two years ago to in 2015

Files updated are:

• https://github.com/kubernetes/website/blob/main/content/en/case-studies/peardeck/index.html
• https://github.com/kubernetes/website/blob/main/content/en/case-studies/prowise/index.html
• https://github.com/kubernetes/website/blob/main/content/en/case-studies/squarespace/index.html
• https://github.com/kubernetes/website/blob/main/content/en/case-studies/wink/index.html

[netlify]

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[mehabhalodiya]

/lgtm
Awaiting another sig docs reviewer/approver to sign off these changes.

[k8s-ci-robot]

LGTM label has been added.

Git tree hash: aac493bb839a6e9b1e112bfbb83886a2be5c73f6

[draksha22]

/assign

[reylejano]

This PR fixes #31424
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: reylejano

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[Babapool]

Thanks @reylejano