Added Database Management Systems (DBMS) section and fixed alphabetic…

[connectwithvanshika]

…al order of some existing sections.

What does this PR do?

Add resource(s) | Remove resource(s) | Add info | Improve repo

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Description

Why is this valuable (or not)?

How do we know it's really free?

For book lists, is it a book? For course lists, is it a course? etc.

Checklist

• Search for duplicates.
• Include author(s) and platform where appropriate.
• Put lists in alphabetical order, correct spacing.
• Add needed indications (PDF, access notes, under construction).
• Used an informative name for this pull request.

Follow-up

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[github-actions]

Linter failed, fix the error(s):

free-programming-books/courses/free-courses-en.md
631:1-645:126  warning  Incorrect number of blank lines between last section and next heading  blank-lines-1-0-2  remark-lint
667:1-673:121  warning  Incorrect number of blank lines between last section and next heading  blank-lines-1-0-2  remark-lint
677:1-681:146  warning  Alphabetical ordering: swap l.680 and l.679                            alphabetize-lists  remark-lint
677:1-681:146  warning  Incorrect number of blank lines between last section and next heading  blank-lines-1-0-2  remark-lint
 685:1-717:95  warning  Incorrect number of blank lines between last section and next heading  blank-lines-1-0-2  remark-lint